Trying the latest ransack

Trying the latest ransack to be compatible with the latest squeel.
Uses ransack 1.3

Uses ransack 1.3 to be compatible with the rails 4.1
update rails_template.rb for rails 4.x

remove the "public/index.html" file only if it exist, rails 4.x don't have this file.
update issues tracker search url in CONTRIBUTING
git ignore bin folder (for rails 4 dev usage)
reimplement `ActiveAdmin::ResourceController performing batch_action` spec
implement missing spec in unit/resource_controller_spec
fix test for 1.9.x
cosmetic
implement missing filter form builder spec #1
implement missing filter form builder spec #2
Easier extending default show page

I would like to add few fields to show page, but keep the defaults.

Passing block to `default_main_content` would make it use defaults + block.
Merge pull request #3357 from timoschilling/specs2

add missing filter form builder specs
Merge pull request #3353 from timoschilling/fix_rails_template

update rails_template.rb for rails 4.x
fix site title of namespaces
Merge pull request #3354 from timoschilling/patch-1

update issues tracker search url in CONTRIBUTING
test yielding block of default_main_content
Add status tag translation for Portuguese
Merge pull request #3368 from brunojabs/master

Add status tag translation for Portuguese
Fix indents in permit_params block

Indents changed to use 2 spaces instead of 1,