Add location & time padding to events

[qchen59]

From ScheduleBot created by lyonva: lyonva#38

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.