Provide python dev tools

[csoriano1618]

Some tools are quite common in Python, say Flake8 and mypy. Would be good to have them included by default, otherwise building all of them in the manifest is quite tedious and tricky. The manifest to build the latest version of them is (note that Flake8 has a range of dependency versions):

        {
            "name" : "typed-ast",
            "buildsystem" : "simple",
            "build-commands" : [
                "/usr/bin/pip3 --disable-pip-version-check install --prefix=/app --no-deps --verbose ."
            ],
            "sources" : [
                {
                    "type" : "git",
                    "url" : "https://github.com/python/typed_ast",
                    "tag" : "1.1.0"
                }
            ]
        },
        {
            "name" : "mypy",
            "buildsystem" : "simple",
            "build-commands" : [
                "/usr/bin/pip3 --disable-pip-version-check install --prefix=/app --no-deps --verbose ."
            ],
            "sources" : [
                {
                    "type" : "git",
                    "url" : "https://github.com/python/mypy",
                    "tag" : "v0.620"
                }
            ]
        },
        {
            "name" : "setuptools_scm",
            "buildsystem" : "simple",
            "build-commands" : [
                "/usr/bin/pip3 --disable-pip-version-check install --prefix=/app --no-deps --verbose ."
            ],
            "sources" : [
                {
                    "type" : "git",
                    "url" : "https://github.com/pypa/setuptools_scm",
                    "tag" : "v2.1.0"
                }
            ]
        },
        {
            "name" : "pytest-runner",
            "buildsystem" : "simple",
            "build-commands" : [
                "/usr/bin/pip3 --disable-pip-version-check install --prefix=/app --no-deps --verbose ."
            ],
            "sources" : [
                {
                    "type" : "git",
                    "url" : "https://github.com/pytest-dev/pytest-runner",
                    "tag" : "2.12"
                }
            ]
        },
        {
            "name" : "mccabe",
            "buildsystem" : "simple",
            "build-commands" : [
                "/usr/bin/pip3 --disable-pip-version-check install --prefix=/app --no-deps --verbose ."
            ],
            "sources" : [
                {
                    "type" : "git",
                    "url" : "https://github.com/PyCQA/mccabe",
                    "tag" : "0.6.1"
                }
            ]
        },
        {
            "name" : "pycodestyle",
            "buildsystem" : "simple",
            "build-commands" : [
                "/usr/bin/pip3 --disable-pip-version-check install --prefix=/app --no-deps --verbose ."
            ],
            "sources" : [
                {
                    "type" : "git",
                    "url" : "https://github.com/PyCQA/pycodestyle",
                    "tag" : "2.3.1"
                }
            ]
        },
        {
            "name" : "pyflakes",
            "buildsystem" : "simple",
            "build-commands" : [
                "/usr/bin/pip3 --disable-pip-version-check install --prefix=/app --no-deps --verbose ."
            ],
            "sources" : [
                {
                    "type" : "git",
                    "url" : "https://github.com/PyCQA/pyflakes",
                    "tag" : "1.6.0"
                }
            ]
        },
        {
            "name" : "flake8",
            "buildsystem" : "simple",
            "build-commands" : [
                "/usr/bin/pip3 --disable-pip-version-check install --prefix=/app --no-deps --verbose ."
            ],
            "sources" : [
                {
                    "type" : "git",
                    "url" : "https://github.com/PyCQA/flake8",
                    "tag" : "3.5.0"
                }
            ]
        },