Rename add_gradle_deps to something more indicating of adding jars

[HosseinYousefi]

          We could introduce some flag that combines the two like `add_gradle_deps` that can be `all`, `none`, `sources_only` and `jars_only`. I think I would mostly want to use `add_gradle_deps: 'all'`. Naming could be improved.

Originally posted by @HosseinYousefi in dart-archive/jnigen#234 (comment)

[HosseinYousefi]

This would be a breaking change now that 0.5.0 is out. Moving it to 0.6.0...

@mahesh-hegde What do you think about the naming? I think we almost always want to have the source when we have it for generation because of the argument naming and javadocs, so the way config is set up needs to reflect this default.

[mahesh-hegde]

I don't really have an opinion with naming. Anything is fine for me.

That said, It's not necessary to add android gradle sources when the code to bind is in project itself.

The JAR in class path however are also used by source summarizer, because it needs a clear picture of every class ever referred to in source.

For example when you refer to android.content.Intent in one of input source files, the javadoc tool need to know what's Intent class. For this, it suffices if Intent is given in the classPath of javadoc tool.

That's the other place class path is used, apart from ASM backend.

[HosseinYousefi]

Not important, there will be bigger changes to the gradle workflow after the introduction of proguard generation.