Unify terminology somewhat.

The class extends the QDDebugService class, _not_ QDDebugServer. It's
right that there is also a QDEngineDebugServer being actually a service
in QtDeclarative, but we should probably fix this one too.

Introduce some more private classes for the coreplugin,
use header include convention
<QtModule/QClass>, de-qobjectify VariableManager.

Task-number: QTCREATORBUG-2318

Reviewed-by: Jarek Kobus
Reviewed-by: hjk

Reviewed-by: Alessandro Portale

To make it work with the HistoryCompleter.

this has only an effect if parsing the previous file failed in a place
with a non-empty stack.

testing data, children and resources properties

This allows more precise unit tests on internals

Task-number: QTCREATORBUG-2339

Inform the user about projects that failed to load as part
of a session.

Reviewed-by: dt

Do not throw projects that failed to load out of the session.
Remember the project file names and append them to the session
again when saving.

Reviewed-by: dt

Only kde-config (and the defined paths) was being considered previously.