GTK2: tabcontrol, less of a gap between tabs and body

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42635 4005530d-fff6-0310-9dd1-cebe43e6787f
LCL: TabControl; better clientarea

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42636 4005530d-fff6-0310-9dd1-cebe43e6787f
LazControls: ExtendedTabControl better clientarea

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@42637 4005530d-fff6-0310-9dd1-cebe43e6787f