From this moment on, we embed a fork of u1db called l2db.

to ease debugging of local servers w/o neededing the Token machinery in
place.

this needs still some extra changes to be fully functional:

- adapt the create-userdb script to work with no auth info.

While parsing the configuration file, if a key doesnt exist we need to
skip it.

All batching code has no effect by default with this commit. Since we
know that this is a dangerous new feature we will enable them only on
our test servers and check them manually before setting it as default
or adding more configuration features.
Use SyncTarget and server conf file to enable it for testing.

Batch support is optional. This commit adds a 'batching' configuration
option to disable it.

Created two methods on the backend to start and finish a batch. A dict of
callbacks is available to defer actions for the last document, allowing
temporary (changing often) metadata to be recorded only once.
Using those methods we will also be able to put all docs in one go on
the CouchDatabase implementation, but that is another step.

Creating a resource from a path to use get_json causes a lot of dirty
code and unexplained things like response[2]. This commit extracts that
logic into a helper to let it more clear about what is happening.