Add leading zeros to 24 hour date formats

[iseulde]

There are a lot of occurrences in core where we use G:i for a 24 hour time format. This leads to weird things like 0:11 and 1:22:33. In general we should never use the G for displaying dates. g should be used for 12 hour time formats since it's a value between 1 and 12. Either it's H:i or g:i.

[iseulde]

Also added a space for g:ia and decapitalised g:i A since we use a everywhere else.

[DrewAPicture]

@dd32: Have an opinion one way or the other?

[dd32]

Agreed. We should only be using either of:

• H:i - [00-23]:[00-59]
• g:i a - [1-12]:[00-59] [am-pm]

which the patch does, I also agree on a space between minutes and the meridiem

The following shouldn't be used:

• h - [0-23]
• G - [00-12] (especially not without the meridiem specified)

[DrewAPicture]

Seems sensible. Patch applies. Moving for commit consideration.

[dd32]

In 31862:

Remove ambiguity in the time display format in core, switches to using 24hr notation where am/pm isn't specified.

• H:i - 09:54
• g:i a - 9:54 am
• F j, Y - January 3, 2015

These shouldn't be used without a/A (am/AM)

• h:i - 01:23
• G:i - 1:23

Props iseulde. Fixes #31121