API: Subsite support for menu of cms (hide admins that don't declare support)  (fixes #101 and #89 )

* Hide admins without subsite support from subsites menu
* Add subsite support to default site areas
* Enable reloading of subsites switcher dropdown when navigating the
site, and when editing subsite areas

API Fix parallel pjax menu fetching for subsites.
- thanks Mateusz!

Delint LeftAndMain_Subsites.js
Merge pull request #104 from adrexia/subsites-ui

API: Subsite support for menu of cms (hides admins that don't declare support) (fixes #101 and #89 )