Change-Id: I8b73d583be1ee7183f4074bce49d5390e38631a2

Reviewed-by: Kai Koehne

We've so far missed the 'QDeclarativeDebug: ' messages, because they
were arriving on an unexpected channel.

Task-number: QTCREATORBUG-4630
Reviewed-by: Friedemann Kleint

Task-number: QTCREATORBUG-4451

Reviewed-by: Kai Koehne

Reviewed-by: hjk

Reviewed-by: Kai Koehne

Add combo box listing toolchains with debuggers to start external,
attach and core.
Another attempt at streamlining engine detection:
Split in detection functions that first collect a list of
available engines by preference, then remove disabled and
wrongly configured engines and use the remaining best.
matching. checkconfiguration is now the central place where
engine detection and config check takes place.

Rubber-stamped-by: hjk

Setting up the debugger connection might fail for a couple of reasons.
Check the application output to show the user a more detailed error
message.

Reviewed-by: hjk

Move tooltip-request handling from DebuggerPlugin into
DebuggerToolTipManager.

Request tooltip only if position changed and close
standard tooltip on success.

Replace old debugger tooltip by a new ToolTipManager which
has a list of AbstractDebuggerToolTipWidget with the functionality
to 'acquire' an engine (display its data) and 'release' it
(store engine data and display them as 'previous') and serialization
to XML session data.
DebuggerTreeViewToolTipWidget implements AbstractDebuggerToolTipWidget
for tree model acting as  a filter on watch models.

Rubber-stamped-by: hjk

reviewed-by: Friedemann Kleint

reviewed-by: hjk

reviewed-by: hjk

reviewed-by: hjk

still racy

This still needs a lot of work and sanitizing.