Add support for LANiS-Online

[johan12345]

https://portal.lanis-system.de/
https://www.lanis-system.de/ueber-lanis/uber-lanis/

Developed by the state of Hessen and used at multiple schools there.

It is questionable if we need to support this as it only parses schedules from other systems to display them, so schools could also provide us the original data from their system.

[AltayAkkus]

LANiS is proprietary, and has a very weird input form, not as elegant as these ones here :D

[johan12345]

Well, the goal would be to parse the output of LANiS to use it as a data source for this (and Vertretungsplan.app), so that would make the result elegant ;)
All other systems we currently support (apart from LegionBoard) are proprietary as well.