[IDEA] 24h notation in filters

[UZ-Brussel-VUB]

Adding the possibility to use 24h notation in the search filter of the message browser and the event browser.

Using the AM and PM notation is very confusing for those not using this kind of hour notation.

Also, the timestamps are shown as 24h in all lists and messages. With this, this is more consistent.

[tonygermano]

This was implemented in #269.

24h notation is now enforced for both the Message Search and Event Search filter inputs.

See #270 about making this a user preference.