Several fixes and optimizations for AdminThemeReno and LanguageSupport. Also added 'overwrite mode' for file/image fields, which lets you upload files having the same name as a file already there, and it will overwrite the existing copy rather than giving it a unique name. This is useful especially when replacing language packs (so you don't have to delete all the files before replacing them). There are also some other minor fixes present in this commit as well.
Add file replacement support for files coming from ZIP files, per the last commit.