Compatibility update for Thunderbird 57+ (currently in beta as of 2018-06-30)

Compatibility Update

Since Lightning 1.0 has (finally) been released as a full version, this is the first official non-beta release for Gantt View as well. The AMO compatibility checker has been automatically updating the compatibility with new releases of Thunderbird, so I won't specifically note the compatibility for this version. I have tested it with TB 9.0

Bugs Fixed:
24597 Day lost when adjusting events ending at midnight
24592 Amendment to Bug 24564 from YearView developer
24564 Gantt View and Year View tabs respond to clicks incorrectly
22129 Make compatible with TB 3.0
21444 Cannot view Ganntview Options on a high res screen - further comments for BUG 21426
21426 Cannot view Ganntview Options on a high res screen

New Features:

- Title Ordinal Override - Allows manual sorting of items using a number at the start of the title. See documentation here. Please let me know if you can think of a more catchy name for this feature!
- Skin updated to match Lightning 1.0 skins

Now compatible with Thunderbird 6.*/Lightning 1.0.0.0b5. Backwards compatibility with earlier versions, including Sunbird 1.0b1, is also maintained.

Other changes:
- Swedish locale (sv-SE) now supported. Tack Mikael Hiort af Ornäs!
- Various code changes for compliance with Mozilla full review standards

Bugs fixed:
- Incorrect day column width on some systems
- Javascript error when less than two calendar items are visible in the view