CMS-3333 Thumbnail displaying

Updated image thumbnail scaling for the images in ContentTreeGridPanel,
Combobox, ImageSelector, ContentSelectedOptionView and in other
elements, that are using NamesAndIconView.
That images will use `scalemax` approach and will be automatically
centered.
Fixed bug with image margin in ContentSelectedOptionView.
Fixed flex align support in the IE.
Merge pull request #713 from enonic/CMS-3333

CMS-3333 Thumbnail displaying