Enable text eliding in base style tabs

This introduces text eliding in Base style tabs when there is not
enough space to draw the entire text label. In addition it removes the
need for clipping completely.

Change-Id: I58be7c88bff275984b97b04c1bd1a942e9d256e0
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>