Fix assistance option on reservation modification

Close #1698
Fix participant not linked to parent contribution

 - prevent ContributionParticipations which are both authors and speakers to
   have their link to the contribution removed when the author is removed but
   the speaker remains.
 - fixes #1596
Add script to fix missing parent contributions

Add a script to find existing `ContributionParticipation` objects with a
missing link to their parent contribution and reset the link appropriately.
Fix rich editor loosing focus on (shift + ) tab

 - prevent the naviation away from the editor when pressing tab or shift + tab
 - fix #1622
Fix disabled "Save" button after copy&paste to min

 - enable the save button correctly after pasting in the minutes editor
 - fix #1653
Merge branch 'v1.9'