Plann

Summary: Misc bugfixes

Fixes

* Things added to the calendar would often bypass the `tz.store_timezone` configuration (defaulted and recommended to be UTC), and rather be stored in the `tz.implicit_timezone` (defaulted to local timezone). Since the local timezone often does not have a valid TZ-identifier (and also, according to the RFC, any non-UTC timezone has to be specified in the icalendar objects), tests would randomly fail dependent on the timezone on the computer running the tests. Credits to github user fauxmight for reporting, fixed in https://github.com/tobixen/plann/pull/8
* Fixes for various other bugs, introduced due to rough development practices for the 0.x-branch. Included in https://github.com/tobixen/plann/pull/8

First release of plann (as of v0.14 it was a part of calendar-cli). Development up until v0.15 has been fast-paced and erratic, prioritizing to "get things to work out well enough for the author". The tool works for me, but has plenty of rough edges.