Eleven - Fixing an issue in ArtistDetail page wherein the hero image

reverts to an unscaled version on subsequent onResume() calls. Also
taking the opportunity to DRY-up ImageWorker#loadImage methods.

To reproduce the bug :
  1. load ArtistDetail for any artist (hero image should be scaled)
  2. Turn screen off and then back on again
  3. hero image should revert back to an unscaled state

Change-Id: I687b192f8480e2cfa628b8ad3f4cb4bdfa6945e9