Cleans up ibc:crawl

- Removes `binding.pry`
- Allows argument passing for degree of separation and last n tweets
Adds totop arrow
Adds missing => in task :crawl
Adds pg_search to Gemfile
Adds indexes to database
Enables PG search extensions
Adds pg_search_scope to Tweet
Enables search in tweets controller
Enables endless scroll
Renders views with JS
Adds dev setup to README