Add .gitignore

* Remove tmp/cache
* Remove development.sqlite3
* Remove log/development.log
Use singular for model name

See http://guides.rubyonrails.org/active_record_basics.html#naming-conventions
Fix formatting

* Remove trailing whitespaces
* Use spaces for indentation consistently
* Make sure every file ends with a newline character
Move deletion of raids into separate action
Move grabbing of user ids to model
Move code for adding and removing users to/from raid into model
Remove code duplication
Replace `for x in range` with `array.each`
Merge pull request #1 from timhabermaas/master

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