Terminate string buffer correctly.

Reviewed-by: dt
Task-number: QTCREATORBUG-3271

the target eventloop emits the correct events when stepping,
(running followed by stop)
its up to the Debuggerruncontrol to fix the raceconditions.
emiting events artificially just makes it worse

further disentangling of debugger dockwidget updates
remove unneeded variable
make updateDockWidgetSettings private
make dockwidget eventfilter slightly less heavy

Also add the alternative way: IOptionsPageProvider, which states
a category, and is asked for a list of options pages for that
category when it is shown.

Task-number: QTCREATORBUG-3131

This is now also postponed to the first switch to debug mode.

Looks like DebuggerPlugin::mainWindow() was used after all.

Task-number: QTCREATORBUG-3292

Add a tooltip for disabled toolchains in the selector dialog.

Kill the debuggee when gdb crashes in stopped state to prevent
the phone from locking up.

Task-number: QTCREATORBUG-3099