fix: shortcuts while editing text item

[letsfindaway]

• While editing a text item, secondary shortcuts like Shift+Ins have not been processed properly
• Instead they have been routed to the board controller
• Add UBApplication::enableEditingShortcuts to enable/disable global action shortcuts for cut/copy/paste
• Disable these shortcuts while a text item is selected
• Reorder and cleanup includes in UBGraphicsTextItemDelegate

Fixes #1367

[letsfindaway]

I reverted this PR back to "Draft" because I now think that it is better to coordinate the editing shortcuts with the focus state of the text item instead of the selection state. Only one text item can have the focus, but multiple might be selected. So I will change this.

My intended target behavior is as follows:

• If a text item has focus, then disable global editing shortcuts, so that they go to the item.
• If no text item has focus, then enable global editing shortcuts, so that they go to the UBBoardController.
• In the UBBoardController remove the check whether a text item is selected. When pasting text, we just have two cases:
  • The text is a URL starting with http: or https:, then start creating a web widget.
  • In all other cases create a new text item.

Note that the latter should happen independent of the selection state of a web widget. The selection state shall never influence paste handling, only the focus state will. For the user, the focus state is indicated by the fact, that there is a text cursor within the text.

[letsfindaway]

ready for review with the above mentioned behavior implemented.