[x] item numbers should be in a different colour in the "compressed" view on smaller devices
[x] Change icons for "chords" and "Sheet music" links to correspond with icons used in items list
[x] A teacher should have less rights than a leader - maybe only adding items?
[x] on very small devices, the action buttons should 'move' into a pull-out menu
[x] consider removing the header row of the items table; then use the icons for the chords/sheetmusic/attachments columns and turn sheetmusic indicator into a link to show it
[x] show more columns on tablet devices - combine title and comment 'earlier'
[x] check if a change of leader/teacher works if they weren't listed in the team before
[x] Add confirmation status to list of team members in popup for "Team" link
[x] error when trying to delete an empty plan (no items) which still has a team
[x] missing "Save" button when entering a note
[x] show team in popup when pointing to "Team" link
[x] when using HTTPS, Firefox doesn't load the Blueletterbible.org refTagger tool (as it's via http)
[x] Send notification when Leader or Teacher was changed
[x] show link to open YouTube song in new tab instead of pup-up
[x] title of YouTube pop-up window should be title of song
[x] add preview of attached file as pop-up when pointing to an item's file attachment indicator