Buttons to use Visuals

Button base case takes over more of the functionality of derived class.
Visuals are now used istead of images.
Dali error added to Builder to be shown if string from json not found

Button Relayout optimised and aligns in 4 directions

Text can be aligned against the foreground using BEGIN, END, TOP and BOTTOM

Positioning of Text and Foreground visual optimised although text not centers if foreground visual present

Button uses visuals instead of placement actors

Tests for Button Visuals and Visual removal with empty map

Allow StageDisconnection to handle visual removal

debug header removed from button-impl.h and now in cpp files.
Fixed map bug in which map was checked for being empty before value was stored in it

Increasing coverage and Removing Internal Button Tests

Internal Tests used a TetButton when it should just use a PushButton.
The Internal tests did not offer any advantage over regular tests so removed.
Tests added to increase coverage and replace Internal tests
Added Wait function to test application

Change-Id: Idb9bccc9ca12a372c3e466fbdb4d8d3d41fb5acf