Centralized the local data, and create new listener mechanism to access it.

Created a permanent SdkManager in UpdaterData (alongside a new AvdManager).
Pages can request a reload (for example on install/delete of a local package),
and other pages are notified of SDK changes to update their display (local
packages, local AVDs, available packages, etc...)

Removed references to UpdaterWindow from the pages (moved some actions
like installArchives and refreshSources into UpdaterData).

Added a new page for the AVDs. Pretty basic for now (only the current AVD
display).

Clicking refresh on the Local pages causes a reload which triggers a
refresh of the listeners pages which properly reloads the AVD page.