Misc improvements to the edit lock functionality

[djplaner]

• Show a timer/indication of how much longer edit lock will remain
  The edit lock can disappear unexpectedly - perhaps too short. Add in a timer to give an indication of when it will expire.
  • Perhaps not too regularly an update to distract the eye
  • Perhaps just a late warning - not all the time.
• In "can't error" warnings
  • add an indication of how much longer the lock will remain (STALE - timelockobtained)
  • add a link to the editing page to enable removal