App becomes unresponsive when removing many items from the Queue using the Multi-select Delete action

[Victor Thompson]

When removing many items from the Queue using the Multi-select Delete action, the app becomes unresponsive. Removing via "Select all" and Delete causes the app to stay unresponsive for what maybe be more than 10 minutes. During this time, the app seems to use ~8% CPU and ~7% of the system memory, which doesn't seem extreme.

To reproduce:
1. Navigate to the Songs tab
2. Tap any item to add the library to the Queue
3. Tap the "Switch to Queue" action in the header (it's the squigly line)
4. Long press any item
5. Tap the "Select all" action (checkbox icon) in the header.
6. Tap the overflow actions area in the header and select "Delete"

Note that after carrying out Step #6 the app becomes unresponsive for what seems to be an indefinite time. I did not wait to let it finish and closed the app after 10 minutes.

[Ubuntu Phone Apps Jenkins Bot (ubuntu-phone-apps-jenkins-bot)]

Fix committed into lp:music-app at revision 774, scheduled for release in music-app, milestone music-app-14.10-week-40