Add script to measure PUT memory usage.
Add scripts to measure backend cpu usage.
Merge remote-tracking branch 'refs/remotes/drebs/feature/add-scripts' into develop
Do not autocreate remote db when syncing (#5302).
Prevent Soledad server from creating or deleting couch databases (#3502).
Do not ensure shared database upon Soledad Server start (#5302).
Remove check for couch permissions.
Merge remote-tracking branch 'refs/remotes/drebs/feature/5302_do-not-try-to-create-db-when-syncing' into develop
Improve client db access script.
Parallelize get_docs on couch backend (#5008).
Merge remote-tracking branch 'refs/remotes/drebs/feature/5008_parallelize-get_docs-on-couch-backend' into develop
Fix raising of auth token errors (#5191).
Merge remote-tracking branch 'refs/remotes/drebs/bug/5191_fix-raise-of-auth-token-error' into develop
do not block on the lock...
move encryption of syncing docs to local db
move encrypt/decrypt functions to crypto module
move symmetric decryption of docs to be db-based too
Extend u1db Synchronizer to allow deferred decryption during sync

I'm splitting the Synchronizer.sync method into the main function
and a second one, that performs the last step (last known gen/trans_id
for a given replica, and PUT with sync info to replica) in a deferred or
inline manner.

This change allows passing the last part of the sync as a callback
to be fired after the asynchronous decryption has finished.
add syncing lock