Changes:
* Allow specification of the homeserver url in the account user when adding
an account. Thus, the following account users are possible:
* `<user><domain>` (defaults to https)
* `<user>http://<domain>[:<port>]`
* `<user>https://<domain>[:<port>]`
* Save sync token for each account in a file. So, only messages newer than
the last sync are retrieved after a restart of the backend.
* Add new commands:
* `bye`: disconnect from the backend.
* `quit`: quit the backend.
* `help`: show list of commands and their description.
* Add and use "chat msg" message format for group chat messages
* Store accounts in .ini file `accounts.ini` in the backend's working
directory. Note: existing accounts have to be re-added to the backend to
be usable with the .ini file.
* Add configuration file support: in addition to the command line arguments,
configuration parameters can now be set in the .ini file `config.ini` in
the backend's working directory.
* Add `loglevel` configuration parameter to command line arguments and
configuration file for setting the logging level to `debug`, `info`,
`warn`, or `error`. Default: `warn`.
* Make daemon python module optional
* Fixes and improvements