Add validation to LValueModel
Change LValueView to only render if its model is valid
Rebuild after saner lvalue widget rendering for invalid model cases
Merge branch 'develop' into feature/issue-91-saner-rendering-for-empty-lvalue-widgets
Fix bad test description for LValueView.render()
Merge branch 'feature/issue-91-saner-rendering-for-empty-lvalue-widgets' into develop