Add angular-feature-flags

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Selectively display details view with feature flag

Integrate angular-feature-flags (there is currently no UI for
overriding feature flags).

This provides a more generic solution than 56bb307e.

As a side-effect, this fixes Bug # 8388

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Merge branch 'dev' into feature/ng-feature-flags

Signed-off-by: Alex Coles <alex@alexbcoles.com>

Conflicts:
	app/assets/javascripts/angular/openproject-app.js
Merge pull request #1396 from opf/feature/ng-feature-flags

Feature flags for Angular app