ie8 fixes for plupload
ie8 has problems with input events, let's simly use an interval
various fixes for plupload/mixitup

- ie8: click on labels won't happen if they are not displayed. And we should keep dropdown open
- ie8: don't use opacity on dropdowns buttons, alpha pngs get screwed
- don't load dropdowns js for mobile version
upgrade to plupload2

build process is not easy (requires node & such) but it could be useful to build a smaller version of the lib (without silverlight or html4 support, for example)
adapt size filter and resize behaviour to new plupload version
make modal much more fluid with ie8

- remove unnecessary filters
- general sibling selector was very slow with ie8 (sometimes applied after severall seconds or not at all)