WIP Major cleanup. Seperation of concerns.

  * ConfigServer - stores global config
  * FileWatcher - watches files and triggers rotor functions
  * WatchGroupServer - stores data about groups
  * EventServer - runs rotor functions for groups

Rotor.Utils provides functions to build and update a file index
Update elixir version
Let WatchGroupServer build file index
Update to-be API in README
Complete Rotor.FileWatcher
Use a shorter method call for getting group info
Remove Rotor.Server
Cleanup rotor.ex
Remove event server
Cleanup watch group server
FileWatcher and WatchGroupServer cleanedup
Set length of changed files as 0
Plan to start file watchers for each group
Tests pass again; Seperation of concerns complete
Fix function names; Update readme; Remove unnecessary function duplication