Bug 912891 - [app manager] Implement a CUSTOM host. r=harth
Bug 912891 - [app manager] Open the toolbox in the app manager. r=ochameau
Bug 912918 - Part 1: Code style cleanups in app validator. r=paul
Bug 912918 - Part 2: Display warnings and errors if both are present. r=paul
Bug 912918 - Part 3: Keep validating after errors when possible. r=paul