Stop place mode when switching to pose mode

See Issue #13923
Make bones annotations visible at startup

Since the code necessary for adding the bones annotations was run at
the creation of the armature widget, the bones annotations were unavailable
until the armature widget was loaded.
To fix this, the code mention above was moved to the logic so it's ran
at start up.

See Issue #13981
Merge branch '13981-BoneAnnotationAtStartUp' into armatures

* 13981-BoneAnnotationAtStartUp:
  Make bones annotations visible at startup
Add Delete Armature Action to context menu

The delete armature action deletes the armature and all its bones. It only
appears when the user clicks an armature node.
It was also the occasion to do a little bit a cleaning in the code.
The two methods calles upon currentNodeChanged() were merged together and
the method named updateArmatureWidget renamed to the simple updateWidget.

See Issue #13923
Merge branch '13923-DeleteBonesOnArmatureNode' into armatures

* 13923-DeleteBonesOnArmatureNode:
  Add Delete Armature Action to context menu
  Stop place mode when switching to pose mode

Conflicts:
	Modules/Loadable/Armatures/qSlicerArmaturesModuleWidget.cxx
	Modules/Loadable/Armatures/qSlicerArmaturesModuleWidget.h