Habapp

- Text header is now properly set (fix for empty strings with Openhab 3)
- Added info about installation through openhabian

- MQTT creates items in HABApp only for messages with persist. Events still get created, even if the item does not exist.
This shouldn't be but could be a braking change.
- Removed many deprecated functions
- HABApp will now use the openhab log folder as a log-default when started for the first time on a openhabian installation
- Reworked MQTT connection so it is now a module, too (Item/Rule interface stays the same)
- Better error message when rule files are executed outside of HABApp
- Added lots of documentation

- items can use ``timedelta`` in ``watch_change`` and ``watch_update``
- Added possibility to specify references in thing config
- ``MqttItem`` does no longer inherit from ``Item``
- Added ``MqttPairItem``:
An item that consolidates a topic that reports states from a device and a topic that is used to write to a device.
- Updated documentation (big thanks to yfaway)
- Removed skipping of ``set_value`` and ``post_value`` in docs

Changes and Bugfixes:
- Fixed a bug where the item watchers would not work after deleting and immediately adding an item again (e.g. *.items file change)
Closes 184
- BaseWatch has now a function which listens exactly to this event
- ItemTimes.add_watch accepts a timedelta, too
- If a file depends on another file that doesn't exist and that file gets added the depending file will be loaded correctly (fixes 186)
- A file with duplicate rule names will no longer break the file load (fixes 187)
- Item registry: renamed set_item to add_item which also raises an exception if the item already exists

Small improvements
- EventBusListener can filter on event properties
- creating/canceling an item watch gets now logged

As always:
- Updated requirements
- added some tests and documentation

- Increase http buffer to 512k (now allows 383k image size)
- reworked ping handling
- Updated requirements

- Ping handling should be more robust
- Fixed an issue where HABApp would not reconnect after an error
- Doc fixes by Rosi2143
- Added DictParameter which can be accessed like a dict
- Reworked file handling:
It is now possible to specify files as dependencies which will be loaded before the specifying file and it is possible to automatically reload a file if another file changed. The topics for file handling changed, too.