Changes base class name to: DatatablesRails::Base.

* Adds `DatatablesRails` module namespace.
* Change in base class name. Generated datatables files will inherit
  from `DatatablesRails::Base`.
* Edits template file in generator.
* Wires RSpec to load all dependencies.
Edits project organization through namespaces and base classes.

* Adds `AjaxDatatablesRails` namespace to organize project.
* Adds `AjaxDatatablesRails::Extensions` namespace to extract helper
  modules that provide behaviors. This namespace will serve as the
  storage place to add compatibility with different ORMs later on.
* Replaces generator with `Rails::Generators::DatatableGenerator`, this
  will include our provided generator in the Rails namespace.
* Removes `FilterdatatableGenerator`. It is not required.
Merge branch 'base'

Conflicts:
	CHANGELOG.md
	Rakefile
	ajax-datatables-rails.gemspec
	lib/ajax-datatables-rails.rb
	lib/generators/ajaxdatatable/templates/datatable.rb
	spec/ajax-datatables-rails/ajax_datatables_rails_spec.rb
	spec/spec_helper.rb