Qbs: Split updateBuildActions

... into a part that sets the internal state and one that updates the
actions.

Change-Id: I78b6b948d2a15aecaeba078d8770a0c52e8ef40d
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Qbs: Clean up updateBuildActions

Change-Id: Id866a37a61cc9c46dcd8683325c2fafc06cec044
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Qbs: Use m_editorProject for signal routing

Change-Id: I6a4453eabd097e81b416f706732926766c7c6c4d
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Qbs: Simplify build methods

Use m_editorProject and m_editorNode where possible instead of going through
the current editor, its document and the nodes.

Change-Id: I252cedccf71a3c9884d0202aae394c42a5e96014
Reviewed-by: Daniel Teske <daniel.teske@digia.com>