Code review comment for lp:~stellarium/stellarium/tz

I very much welcome a thorough re-work on the timezone issues, the many bug and wishlist items speak for themselves.

I had no time for a thorough test so far. Do you want to merge now and run public testing for a few weeks on the new trunk betas (and of course fix a few rounds in trunk), or have some testers on this branch and merge only when all is done? Can you publish betas from this branch?

I think some extra TZ settings options can be built into the main program's location panel. (This can become a bit larger. Also the map is very small on FullHD and higher-resolution screens.) There is no use to have a plugin when you must have it activated anyway for really basic operations. The configuration panel is more easily reached in this way.

Some things that can hopefully solved with IANA's TZ database:
DST rules for "Continent/City" timezones. In various countries, DST was introduced at some point in the 20th century. (e.g. WW1, WW2, energy crisis in the 1970s). It would be great if all times can be produced here.
Timezones were introduced around 1886, but not everywhere. Some standardisations were available previously (e.g. Railway time). The current 1886 limit may need a second thought.

Some useful options:
Have a tick (default=active) "System Defaults". This uses time zone of configured location.
Use system settings, but disable DST.
Set timezone as UT offset (15 minute steps)
Use Local Mean Solar Time. This should be default until 1885 (or we find some other meaningful date?).
Use Local True Solar Time (i.e. also add Equation of Time!) This may be useful for historical research. LTST use should be marked somehow in the bottom bar.

In any case, UT+HH:MM should be visible in the bottom toolbar like it is now. Maybe print TZ name or "LMST" in addition?