feature: auto fix visibility based off the error

[mattem]

Based off the visibility errors generated by bazel, eg:

ERROR: /blah/BUILD.bazel:0:00: in py_library rule //foo/bar
 target '//baz:baz' is not visible from target '//foo/bar'. Check the visibility declaration of the former target if you think the dependency is legitimate

Suggest auto fixes to the user if they accept that the dependencies are infact, legitimate.

[alexeagle]

Simple method is just add //foo/bar:__pkg__ to the visibility attribute of //baz:baz without taking any care about package_group targets or coalescing into __subpackages__.
Maybe that's fine if we leave a comment on our new entry that it was auto-added from the CLI, then at least it's more clear that it wasn't done by hand and therefore could use some curation.

[f0rmiga]

Done in #34.