(bug 42995) Basic error handling for claim/snak UI

When saving/removing a claim/snak fails (the API returns an error code), the value part of the
snak is highlighted an a tooltip containing information about the error pops up.

Change-Id: Ib630fe65adcb704dbafbe6958650c4464986b24c
Merge "(bug 42995) Basic error handling for claim/snak UI"