feat: Add all time zone names

[l0b0]

This includes all the "canonical" time zone names from https://en.wikipedia.org/w/index.php?title=List_of_tz_database_time_zones&oldid=1047681771 plus UTC.

Unfortunately GNOME doesn't deal with this appropriately, so I'll have to create a sub-menu type thing.

Closes https://github.com/mibus/MultiClock/issues/14.

[mibus]

Yeah, the UI aspect was why I hadn't done anything here. I'd be thrilled to add this, if the submenu idea pans out.

[l0b0]

@mibus Do you know how to navigate the documentation? I couldn't find where Lang.Class.menu.addAction is documented.

[mibus]

I do not. When I was last doing work on the extension, I just downloaded all of the related source code (gnome-shell, I don't remember if there was anything else) and did a lot of grepping.

[Demetrio92]

Absolute must-have.

[l0b0]

Anyone willing and able to take over this? The code is completely unfamiliar to me.

[l0b0]

Project seems to be dead; closing.