MQTTClient: Added a topic_matches() method

- Also added a keepalive argument to the connect() method
Added a loglevel shell command

Allows to change the level of a logger
Added a -v/--verbose argument to pelix.shell.console (ran as script)
Replaced apt-get by pyenv install

Travis-CI removed the deadsnakes repository and replaced it by pyenv to
install custom Python versions.
Travis-CI configuration tests...

Now using the TOX_ENV trick
Merge remote-tracking branch 'origin/dev'