Fix: Syncer synchronizes only once

[sunkup]

Purpose

Fix the Syncer not synchronizing anymore after the first initial sync.

For more see #909

Short description

In #881 we used the same hashmap (remoteCalendars, remoteAddressbooks, ...) for supplying collections to the sync manager and to determine whether a new local resource (calendar, address book, task list, jtx collection) should be created for a new found remote collection. This PR introduces a second hashmap (newCollections), copying from the initial one (remoteCollections) to determine new remote collections by subtraction. The original hashmap (remoteCollections) will then be used to provide the collection to the sync manager when syncing.

This PR will also close the acquired provider in the abstract syncer, which was forgotten in #881.

• Rename the different remoteCalendars, remoteAddressBooks, etc. collection HashMaps to generic remoteCollections
• Use a separate HashMap newCollections to determine new remote collections
• Create new local resources (calendar, address book, task list, jtx collection) from newCollections
• Use remoteCollections to provide collections when syncing to sync manager.
• Close content provider after sync in syncer

Checklist

• The PR has a proper title, description and label.
• I have self-reviewed the PR.
• I have added documentation to complex functions and functions that can be used by other modules.
• I have added reasonable tests or consciously decided to not add tests.

[rfc2822]

Works!

The provider.close() in the sub-classes is redundant, isn't it? Looks as if we could remove it from the sub-classes. Syncer acquires the client, so it's responsible for closing it.