Add conference talks and auto-update room descriptions

[schrockwell]

What's new?

• Add Talk schema to represent conference talks
• Add CSV import for talks (see priv/schedule.csv)
• Add Talks context module for managing this stuff
• Add RoomTalkUpdater which polls the DB every 60 seconds and broadcasts new room info to the chat lobbies

It's crunch time and I'm running on like 12 hours of travel and 2 hours of crappy hotel sleep so no promises on the quality of any of this code.

[shadowfacts]

Merged and implemented the changes I mentioned manually (and tested them):

• https://github.com/liveviewnative/elixirconf_chat/commit/d8d7815b39531fefb7385afaf5dc2a21f7e46e82
• https://github.com/liveviewnative/elixirconf_chat/commit/856b314b52d7f59a6a76c55438abb1c739878975