The correct pattern is this: The actions in the build menu are supposed
to be for the startup project. They should use the global context and be
manually hidden/shown if the startup project changes.

This fixes a crash on assigning keyboard shortcut to the edit files
context menu action.

The slot connected assumed that the action could only be triggered via
the context menu. By using ProjectTree;:currentProject() the code now
works even if the project tree is not actually focused.

It also fixes that the "Run CMake" action was shown even in the build menu,
even though a non cmake project was the startup project.

Change-Id: I0bb8086d8b1078b4c71c3b5ba9d7f8596757e724
Task-number: QTCREATORBUG-14728
Task-number: QTCREATORBUG-14768
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>