ManageSieve: make sieve_formattime() parse all time-formatters PHP does.

[bennet0496]

Roundcube's $config['time_format'] understands all PHP time and especially timezone format specifiers listed in the PHP docs; however, sieve_formattime() that used this value via rcmail.env.time_format does not.

Therefore if the config value e.g. is $config['time_format'] = "H:i T" to include the abbreviated timezone name (which works else where, like the message list), then forms using sieve_formattime(), the OOO form, will generate times like "6:00 T" and so on

This causes the actual time be set to "Tango Time", i.e. UTC-7

Which for users outside of UTC-7 is unexpected behavior.

Therefore I changed sieve_formattime() to understand any formatter that may reasonably (or unreasonably, like microseconds or Unix Time. But never say never) be configured by an admin or user. For the timezone values, I opted to pass these values from PHP to JS via set_env() as in JS these values are extraordinarily hard to reliably to obtain without additional libraries.

I also changed some thing at the beginning of sieve_formattime() that looked odd to me. Like per-declaring all variables. And actually used the value that h would have been in the g and h cases. But I'm also happy reverting these changes if they are undesired.

[pabzm]

Thank you very much for your contribution!

Your solution is solid, but please don't include the drive-by improvements into the same PR (or at least not into the same commit). It makes it unnecessary hard to comprehend, which changes are related.

Could you correct that?

[bennet0496]

I removed the drive-by changes to the 12h format. Do you want the fix for that here as another commit or do you want another PR for that?

Also I removed the Unix timestamp, because looking over it, it doesn't quite makes sense here, because of the implicitly included date.

[pabzm]

Please open a new PR for the 12h-changes. Thank you!

[pabzm]

Great, thanks! Now all that's missing from my point of view is an entry to the Changelog. Would you mind adding one? (Feel free to decline!)

@alecpl Any thoughts on this?

[bennet0496]

Is the entry ok like this? If not I will revert it :)

[pabzm]

Perfect, thank you! 👍