Implement 'maintenance performed' logging for OCPL

[following5]

OCDE and OCPL have different logic for indicating that a cache does not / no longer need maintenance.

• OCPL has "maintenance performed" logs, which can be logged anytime by anyone.
• OCDE has "cache is ok" logs, which can be logged anytime by anyone.

OCPL has copied the GC logic here, while OCDE has chosen to improve it. E.g. "needs maintenance" sometimes is logged erroneously, and then there is no need to perform maintenance, but just to indicate that the geocache is ok. Also, a good state of a geocache can be confirmed by "cache is ok".

OKAPI so far only reflects the OCDE logic by the needs_maintenance2 option. I am not sure how to integrate the OCPL "maintenance performed" log type. Espacially, when considering that it is also used to indicate "there was no need for maintenance" after erroneous "needs maintenance" logs.

[following5]

See related issue #374, which is about retrieving logs. This here is about submitting.