Signal2html

* Add support for clickable urls (thanks to sbaum for reporting
[37](https://github.com/GjjvdBurg/signal2html/issues/37))
* Display more message metadata (thanks to ericthegrey in
[33](https://github.com/GjjvdBurg/signal2html/pull/33))
* Add header to threads as in the app (thanks to Aztorius for suggesting this
in [39](https://github.com/GjjvdBurg/signal2html/issues/39))
* Minor formatting fixes for thread messages

* Bugfix for resolving recipient names for database version 108 and higher
(thanks to sbaum for reporting
[34](https://github.com/GjjvdBurg/signal2html/issues/34)).

* Bugfix for non-existent recipients (thanks to ericthegrey
[30](https://github.com/GjjvdBurg/signal2html/issues/30)).
* Expand color palette to match Signal (thanks to ChemoCosmo for reporting
this (see [30](https://github.com/GjjvdBurg/signal2html/issues/30)).
* Support messages for video calls and key change (thanks to ericthegrey
[29](https://github.com/GjjvdBurg/signal2html/pull/29)).

* Add support for mentions (thanks to ericthegrey)
* Fixes for output filenames and directories
* Minor cleanup

* Improve version tests (thanks to ericthegrey)
* Add support for reactions (thanks to ericthegrey)

* Clean up code using an Addressbook class for recipients (thanks to
ericthegrey [15](https://github.com/GjjvdBurg/signal2html/pull/15)).