Fancy event locations

Related: #104

## Use cases

- I want to be able to click on a location in either StartSCH or in my Google Calendar and have it open Google Maps at the right location.
- BME Egyetemi Napok: I want to be able to filter events based on location

## Implementation

- We would probably store a coordinate and a textual representation. It'd be nice to open the right POI in Maps instead of just opening it based on the coordinates.
- .ics supports fancy location stuff but idk if it's actually implemented in any of the calendar apps

Start by reading the related issue #104 and tracing how event locations are currently represented, exported to Google Calendar, and exposed for event filtering. Compare the stated Google Maps and BME Egyetemi Napok use cases with the existing .ics behavior. Done should cover an agreed location representation, map links, and location-based filtering.

Written by the indexing model from the issue text.