Add rubocop style checks.

Rubocop  statically checks code using the [Ruby Style
Guide](https://github.com/bbatsov/ruby-style-guide). This guide is
opinionated in a lot of regards but it has become the most popular and
agreed upon guide.

I have added a custom rubocop file to tweak some
things to Rails-specific style, and I also ignore checks on some important
files.

All of these can be run with the rubocop gem from the terminal.
Since we have a very large number of corrections, I used rubocop to
create a todo file. This makes it easy to enable style checks in small
chunks so that commits are smaller and easier to follow.
Add rubocop to rake file.

I added rubocop to the rakefile to make it's use a little easier for
devs that just want to run file checks. This will also be easier to run
from a CI system in the future.

The command to run the style tests is
rake rubocop
Merge branch 'dragoon/addrubocop' of https://github.com/drag00n/phishing-frenzy into drag00n-dragoon/addrubocop

Conflicts:
	Gemfile
	Gemfile.lock
Merge branch 'drag00n-dragoon/addrubocop'