Add support to disable features with command line argument

[NotTheEvilOne]

What this PR does / why we need it:
The newly added command line argument --disable-feature supports removing feature dependencies normally added to an image.

Which issue(s) this PR fixes:
Closes #17

Release note:

Add `--disable-feature` as command line argument

[nkraetzschmar]

Making the set of features based on command line arguments is bad for 2 reasons:

1. The artifact cname no longer uniquely identifies what was build: two builds, one with --disable-feature X, one without, would have the same cname, but be fundamentally different artifacts)
2. The builder can build multiple artifacts in one. So ./build A B C, where A, B, and C are all partial cnames is totally valid. Now in this syntax, which target does --disable-features apply to? All? Just the one directly after it? This introduces ambiguity.

This should really be done via pseudo features that exclude the unwanted features. So instead of --disable-feature x, there should be a feature/modifier _noX which just has a info.yaml with

description: "exclude feature X"
type: flag
features:
  exclude:
    - X

[NotTheEvilOne]

Agreed so the original issue request report should be closed :)