Only show "add connection" button if relevant

- We don't want to present the user with the "add connection"
button if the user doesn't use the account that provides the
service

- Check if app contributing the account type is disabled or not

- Check if there is an activity to handle the "add connection"
intent

- Check if there are raw contacts in the database with that
account type

- Store this in a cache, and refresh it after a certain
period of time (i.e. 1 second) using an AsyncTask.
This is to prevent computing the list each time the contact
is loaded (which can happen many times especially when looking
at a detail page during a sync).

- Make sure public AccountTypeManager methods
first check ensureAccountsLoaded()

Bug: 5398529
Change-Id: I004f9562a587035a3168aaddb6eb43710fd201e6