Upgrade to Rails 4.1.4

* Upgrades Rails to `4.1.4`
* Upgrades `will_paginate` to `3.0.7`
Spec and fix for Administration::DashboardsController
Add secret_key_base to travis.yml
Remove old disable_implicit_join_references setting.

http://guides.rubyonrails.org/4_1_release_notes.html

> Remove implicit join references that were deprecated in 4.0.