Etc. updates

I didn't bother to branch out this time, as it doesn't seem to serve any large purpose.

These changes are largely cleanup. I have made some changes to code style, in accordance with the Ruby Style Guide [1]. Other changes include cleaning up the relation between User and Order and related code implications. I've also added authentication tests and completely replaced `my_profile.feature` with unit tests.

I recommend reading through the commit messages and reading through the diffs.

[1] https://github.com/bbatsov/ruby-style-guide