Add location & time padding to events

So that scheduling takes into account transportation time. Say:

- Event 1 is on location A
- Event 2 is on location B
- Event 1 and Event 2 are 1 hour apart
- Location A and location B are a 45 minute drive apart
In this scenario, scheduling a 30 minute event between E1 and E2 should fail, as you only have 15 minutes available. Worse if the new event is also on another location.