Disable "Linked With Parent" checkbox for top-level bones

See Issue #13698
Merge branch '13698-DisableParenthoodCheckboxForTopLevelBones' into armatures

* 13698-DisableParenthoodCheckboxForTopLevelBones:
  Disable "Linked With Parent" checkbox for top-level bones
Smaller step only for the direction combo box

See Issue #13922
Merge branch '13922-SmallerStep' into armatures

* 13922-SmallerStep:
  Smaller step only for the direction combo box
Delete bones option on armature nodes too

So far, the "Delete Bones" option the the bone tree view only worked on
bone node. However it was also available for armature nodes although it
did nothing.
This changes the behavior of the last case, where it will delete all the
bones of the armature without deleting the armature itself.
The behavior when clicking on a bone is preserved (it will still delete
the current bone and all its children).

See Issue #13923
Stop place mode upon bone/armature deletion

When in persitent mode, the user can still delete armature or/and bones.
This creates a weird state where the user still is in adding mode
although he cannot. To prevent this, evrytime the user deletes a bone or
an armature (or change to another armature), the widget switches back to
normal interaction mode.

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

* 13923-DeleteBonesOnArmatureNode:
  Stop place mode upon bone/armature deletion
  Delete bones option on armature nodes too