(bug 42997, bug 44291) Handle invalid values in statements ui

Depends on change I26cbd7e4 and change I460cfc67 in DataValues extension.
Saving will not be possible anymore while the snak is invalid.

- patch set 2: Rebase
- patch set 3: Adapted change set to recent changes on master branch

Change-Id: I4515a30093e18eb66d5938e50d91927306067069
Merge "(bug 42997, bug 44291) Handle invalid values in statements ui"