User-configurable time format

[cpinkham]

Is your feature request related to a problem? Please describe.
I would like to have the ability to display a 12-hour time format without the AM/PM indicators to save space.

Describe the solution you'd like
I am looking for your preference on how to implement so I can submit a pull request. I can either allow generic strings like 'h:mm' in the current time_format field which would mean disabling the "must be '12' or '24'" sanity check in types.js or I can create a new optional time_format_str field which is a string type and doesn't have any sanity check in types.js.

Describe alternatives you've considered
I am currently running a patched version which enables this functionality using a new time_format_str field.

Additional context
Not much to show here:

time_format: h:mm

OR with a new field:

time_format_str: h:mm

[pkissling]

i think it makes sense to introduce time_pattern property similar to date_pattern

[cpinkham]

OK, thanks. I didn't even notice that date already supported something like this. I'll take a look at it and see about generating a pull request for time.

[pkissling]

Released 2.1.0 including #242