Add support for version specific drawable directories

[casolorz]

Basically I was trying to create the scaled drawables for my notification icon which go under the -v11 folders and didn't see any option to do that.

I think a simple way to do it would be to have a dropdown above the "Dimens:" which says something like "target version:" and then have options like "all","v22","v21", etc.

Thanks. Awesome plugin!