Sync: use constants instead of authorities where applicable

[rfc2822]

We have many locations where we use the various authorities in the meaning of the Android sync framework to specify what to synchronize.

However, we don't use the sync framework anymore for most syncs, and also the mapping of authorities to what shall be synchronized is not 1:1:

• Address books authority (R.string.address_books_authority) – Needed because main accounts are not synchronized with the ContactsContract.AUTHORITY. This is because a main account doesn't contain contacts directly, but only address book accounts, which then contain the contacts. So if we want to sync all address books of an account, we currently use the address books authority.

• CalendarContract.AUTHORITY – Currently used as intended without extra workarounds.

• Task authorities for jtxBoard, tasks.org and OpenTasks – Instead, we often want to just have "tasks". For instance, there should be a tasks sync interval, and not a jtxBoard sync interval, tasks.org sync interval etc. So most occurrences of these authorities will have to be replaced by a "tasks" constant.

• Go through all occurences of authorities and see whether the location really requires an authority in the sync framework meaning or should be replaced by a {contacts, calendar, tasks} enum or something like that.

  • Probably change AccountSettings sync interval getters/setters to not require authorities.
  • Probably change the workers to accept the enum instead of authorities.

• Check/adapt TasksAppWatcher