Bump gems to support ruby 2.1, use rspec-3 syntax in specs

Also try to make acceptance test more reliable
Run travis tests with 2.1.4, too
Add pry debugging gems to development group
render activity messages in oulu
Include author in activity message
Use byebug with ruby ~> 2.0.0 and debugger with ruby ~> 1.9.0
Implement discussion events
Simplify code
Render messages to threads