Fix meeting-hours caching

[ben9583]

The meeting hours API has some endpoints that are time sensitive (/api/meetings/current, /api/meetings/next) that were previously cached for a long time, meaning the API would return out-of-date results for both of these. This pr fixes that by using a 5-second periodic call, which is also the method the computer availability API uses.

The endpoint /api/meetings/list is not affected by this change.

[Kalissaac]

oh wait the tests failed