[Lazarus] New TTabControl

[Felipe Monteiro de Carvalho]

Hello,

I just wrote a new implementation for TTabControl to fix the control
hierarchy. I expect it to be 100% backwards compatible and at the same
time have the correct class hierarchy.

The implementation itself remains basically the same, it is just
adapted to the new position which it occupies in the hierarchy. The
control does not have its own WS implementation, but instead it relies
on TCustomTabControl and on Themes.

People interrested in this control please test by adding
-dLCL_NEW_TABCONTROL to LCLBase. Then TTabControl will be replaced
with the new version.

-- 
Felipe Monteiro de Carvalho