Fix server initscript location (#6557).
remove unused imports
remove taskthread dependency
use max cpu_count workers on pool
reorganize pragmas, stub SQLCipherOptions object
move public api to its own file
Refactor soledad api to use async db

* add examples and benchmarks
* remove autocommit mode, allow wal disabling
* lock initialization
* make api use async calls
Separate soledad interfaces

* Separate local storage, syncers and shared_db
* Comment out unused need_sync method
* Use twisted LoopingCall
* Create a threadpool for syncs
* Return deferred from sync method
* Do not pass crypto to SQLCipherDatabase
* Pass replica_uid to u1db_syncer
* Rename / reorganize some initialization methods
Adapt sqlcipher tests to new api.
working sync-threadpool

* Completed mapping of async dbpool
* Fixed shared db initialization.

Stuff To Be Fixed yet:

[ ] All inserts have to be done from the sync threadpool.
    Right now we're reusing the connection from multiple
    threads in the syncer. I'm assuming the writes are automatically
    locking the file at the sqlite level, so this shouldn't pose a
    problem.
[ ] Correctly handle the multiprocessing pool, and the callback
    execution.
add soledad sync example
add syncable property to shared db
minor naming/documentation fixes

after drebs review
Save active secret on recovery document.
Standardize export of secrets to avoid miscalculation of MAC.
Fix interruptable sync.
Adapt tests for new api.
Cleanup unused import.
Several fixes in soledad api.

  * Allow passing shared_db to Soledad constructor.
  * Close syncers on Soledad close.
  * Fix docstrings.
Several fixes in adbapi interface:

  * Get replica uid upon U1DBConnectionPool initialization.
  * Fix docstrings.