Default build and overrides

[KatieHarris2397]

1. If user does not provide any build specifications in builder.yaml Builder should use the default "assumed language" build command
2. If a buildcmd is provided Builder should use it as the build command
3. If a buildfile is provided without a buildcmd Builder should use the build file with the default build command
4. If a buildfile and a buildcmd is provided Builder should use the build command given
5. If a buildtool (where user is specifying make, gradle, maven, etc.) is provided, Builder should use the build steps defined for the specified tool (i.e. if "maven" or "mvn" is provided as the build tool, Builder should run the command mvn clean install)