Do not remove bin folder in Gradle projects

[Lipen]

#81 introduced support for Gradle projects, however I would advise against counting the bin folder as part of the "build files". AFAIK, Gradle only uses build folder for artifacts and .gradle for Gradle wrapper.
I do believe, many people build/download "external" binaries and put them in the bin folder. Sometimes, this is a part of automatic build process, and the removal of such binaries is "revertable". However, I also believe that some people (e.g., me, at least) do this manually, since it is being done only once. For example, in the cases when these binaries are necessary only for integration tests or for some extra functionality.

Long story short, bin folder is definitely should not be considered as "build files".

[tbillington]

Thank you for the detailed explanation, that makes sense to me.