Using the same logic as the single Export/Import commands, implement the
entire backup command by exporting all the serializable classes into a
single json file.
To select the correct class upon import, save a new property on the
backup json, the class_, which contains the name of the class to be
imported.
Fix the note serialization.
Pickling directly from a DB object will also save DB related attributes,
namely the state of the object. When exporting values from a DB select,
they will be in detached state, which means on the import, the session
will not insert the object back into the DB, it already assumes they are
there.
The new command ImportCommand takes a Serializable type, from which it
can call the deserialize method to generate a DB ORM type. The
Serializable interface also declares the serialize method.
(De)serialization moved to the ORM types, due to the inability to
properly use overloading.
Possible improvement for the future is to merge serialization
information on JSONDecoder/Encoder classes.
Adds a MockClient with the in-memory SQLite DB which can be used by
tests.
Most types export/import functionally tested using two DBs and comparing
entries.
CSV is not a good format, since it does not have a good support for
complex types, e.g. lists.
It served when the exported format was only a linear transaction, but it
is not worth the extra work around it anymore.
