add omniauth to Gemfile
use github as first omniauth strategy
remove test folder
generate authentications table
set up associations for user and authentication
add index for uid and provider combo
add uniqueness validation for uid/provider and provider/user combination
complex implementation of auth callback (TODO: move to smaller methods or a service class)
destroy other records when a user is deleted from the database
refactor complex omniauth login callback to its own service class
add link to github login in login page
add facebook omniauth strategy
Revert "add facebook omniauth strategy"

This reverts commit f5e39e1497c62159e84723d0b1e12fcc9c580e5c.
add linkedin to omniauth strategies
add linkedin login link to new session page
use a proc to determine if has_secure_password should validate or note
add specs for omniauth callback
add missing spec for application helper
add specs for omniauth handler service class
fix failing specs