Added .jshintrc

- Added `.jshintrc`
- Also fixes a few JSHint warnings in files app
- Added "global" comment on top of files app to suppress warning and
  also inform devs about what globals are use

I've started to use JSHint and (using Syntastic in vim) on another branch and would like this to go in earlier (than my other big PR). I think it is useful, especially that it can also find some coding errors.
When using globals, you need to add a comment at the top of the file in the form:

`/* global OC, FileList, FileActions */` to suppress globals warnings. This is also a neat way to show all globals that are used in one place (and hopefully one day getting rid of globals altogether).

Your IDE might be able to pick up the `.jshintrc` in the project or you might need to configure it to do so.

@DeepDiver1975 we could integrate this in Jenkins later but I think we should be tolerant with some of the rules (like the max 80 characters) so they should only be treated as warnings most of the cases.

Please review @DeepDiver1975 @karlitschek @jancborchardt @Kondou-ger @bantu @kabum