Add 'Close' Continuity

[kmdurand]

Right now there are only "mark time" commands. Since the Online Viewer can handle "stand" commands, we should be able to export them.

[kmdurand]

Interesting: you can actually use a "close" operation in CalChart, but it just translates to a mark-time token in the grammer

[Ethan-Stone1]

Currently able to manually enter Stand And Play as a Continuity (in the Print Continuity section); however, since CalChart only has a MarkTime option, MT still shows up on the online viewer.

In the following image (taken from Rihanna Show 2023) the top box represents what is to be printed, with the bottom box auto-populated by CalChart. Ideally there would be a Stand and Play option in the CalChart continuity dropdown which when selected would show as Stand and Play on the online viewer.

(https://github.com/calband/calchart/assets/14023189/0311660b-fdee-41f1-bad5-9d17cfcd6c71)

[rmpowell77]

Fixed in #490