Remove gemfiles, Gemfile.lock from version control

Remove gemfiles from Travis.
Simplify Appraisals

* Test latest Rails 3 version against Ruby 1.9 and latest Rails version
  that supports Ruby 2.
* Force Appraisal to build gemfiles for Travis.
* Use two-digit precision with pessimistic operator for closer adherance
  to SemVer.
Restrict Ruby support to MRI 1.9, prepare for 2.0
Consistently use ~> 'maj.min' on dev dependencies

Upgrade Rake, Strong Parameters.