bugfix: vcross times update

Summary:
bugfix: vcross times update

  * vcross::QtManager::setModels must return true if time set has changed

Test Plan:
open vcross, select two models with different forecast times and
 check that the time box is updated

Reviewers: #diana, lisbethb

Reviewed By: #diana, lisbethb

Subscribers: YngveE

Differential Revision: https://phab.met.no/D45