Core: Static pattern for ProgressManager, clean up all users

Change-Id: I4af8793ca69a3af9e99baeb7c31dad3864266f91
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Core: Remove ICore::appMainWindow()

Not seriously needed.

Change-Id: Ide001ce83f9e86306f5d13597716d2ab0d50abbf
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
ProgressManager: Remove unused constructor parameter

Change-Id: I0c27f54c813cfba1c9e940b2431a0950fd1e4b8d
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Core: Remove unused functions from MainWindow

Change-Id: I4f399aa01fc1ef27e35d759ccc74584b8df1ca07
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Core: Remove MainWindow::editorManager() accessor

Change-Id: Ic22cb1b0313ba51fa144b31117c6b005da0a4bff
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>