Nuqql-slixmppd

Changes:
* Use nuqql-based as dependency and adapt to nuqql-based changes
* Add setup.py for installation and package distribution
* Add python type annotations
* Restructure code

Changes:
* 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

Changes:
* Add group chat support and messages:
* list chats on account: `account <id> chat list`
* join a chat on account: `account <id> chat join <chat>`
* part a chat on account: `account <id> chat part <chat>`
* send a message to a chat on account: `account <id> chat send <chat> <message>`
* list users of a chat on account: `account <id> chat users <chat>`
* Cleanups, fixes, and improvements

Changes:
* Add account status message:
* Set current status with: `account <id> status set <status>`
* Get current status with: `account <id> status get`
* Use stricter permissions for account, log, and sock files

Changes:
* First/initial release.