Debugger: Simplify Tooltip manager interface

The Editor itself is not really used.

Task-number: QTCREATORBUG-10358
Change-Id: I94620ed7b3b1d6b02c4eef2a359f991217b0a00b
Reviewed-by: David Schulz <david.schulz@digia.com>
Debugger: Apply static pattern to DebuggerToolTipManager

Change-Id: I49869c393b922da75572959973b917894f93f4ec
Reviewed-by: David Schulz <david.schulz@digia.com>
Debugger: Simplify DebuggerToolTipEditor convenience structure

Change-Id: I0e86bb657a225cdf2d915b5d1f9526856064e92d
Reviewed-by: David Schulz <david.schulz@digia.com>