Revert "Changed Username to Email on form"

Turns out that the Username is what's used after all.

This reverts commit b613c625717dfae5b435fed6234d9b6f81256065.
Revert "changed Username to Email"

Gave Bobbi bad information, reverting commits based on same.

This reverts commit 74d1cc0ae0a97b6c3e3148ceda53e6e32a0cf20f.
Added pry gems to test, for use in debugging Cucumber steps.
First pass, working destroy for persisted sessions.
Changed bootstrap mechanism from sprockets requirement to Sass @import, so clearfix() and other mix-ins will work.