support for multiple tags

[kir12]

certain events e.g. the guest concerts should have both the "guest" and the "performance" labels.

• in events.csv separate with periods "."
• split by periods "." when reading in the CSV file
• modify filtering and rendering to account for possibility of multiple events

[kir12]

dependant on #23

[kir12]

with the cutover implemented early, this issue is now fair game