DUI: Better way of loading icons.

I found the fastest way of loading icons. EB would be pleased ^_^

# Reviewers
@Benglin,@vmoyseenko, please take a look.

Link to YouTrack:
[MAGN-4616](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4616) DUI: Some library items take long time to open up
Instead of ResourcesReader I used ResourceManager. It's much faster.