reduce double code in devise_generator.rb
code reduce in Views::Pages::Index#title
tests for ActiveAdmin::Views::Pages::Index#title
Use `sort_by` instead of `sort_by!`

`sort_by!` and other mutator methods are blacklisted as of Ruby on Rails
4.1.0.rc2 and now yield `NoMethodError`.

References:
* https://github.com/rails/rails/commit/d4ee09c
Merge pull request #3064 from jgorset/fix/undefined-method-sort-by!

Use `sort_by` instead of `sort_by!`
Merge pull request #3052 from timoschilling/pages_index_codereduce

code reduce in Views::Pages::Index#title
Update README with info about dependencies for Rails 4.1.
Merge pull request #3066 from sbleon/rails41_install_doc

Update README with info about dependencies for Rails 4.1.
Merge pull request #3050 from timoschilling/devise_generator_code_reduce

reduce double code in devise_generator.rb