(Bug 44765) Add user-select:none to wb-u-toolbar and -group

This makes the toolbar text unselectable and it will not be copied
in cut-n-paste operations.

Note that this doesn't work quite this way in all browsers.

Change-Id: I61b8d49bd60d333768072e5d0abfed04a99715b3
Merge "(Bug 44765) Add user-select:none to wb-u-toolbar and -group"