Resolve "(fix and) start running webui unit-tests"

Closes #164 (closed)

The remaining failing tests are:

• AppDaemonsStatusComponent: TypeError: Cannot read property 'details' of undefined
• AppComponent: Expected undefined to equal 'Stork'.
• AppsPageComponent: TypeError: this.handler.handle is not a function
• Bind9AppTabComponent: TypeError: Cannot read property 'subscribe' of undefined
• BreadcrumbsComponent: TypeError: this.items is not iterable
• HaStatusPanelComponent: TypeError: Cannot read property 'state' of undefined
• HaStatusComponent: Error: Required parameter id was null or undefined when calling getAppServicesStatus.
• KeaAppTabComponent: TypeError: Cannot read property 'subscribe' of undefined
• LogViewPageComponent: TypeError: Cannot read property 'subscribe' of undefined
• PasswordChangePageComponent: Uncaught TypeError: params.get is not a function thrown

This MR also adds dev guide section and new unit tests for menu items visibility.