batch actions allow add a proc to form parameter.
Allow to duplicate 'Batch Actions' button at the bottom

Switches 'Batch Actions' button selector from ID-based to class-based which allows to use multiple (duplicated) batch buttons. Duplicating button at the bottom speeds up batch operations on large tables (user don't have to scroll back to the top).

The following monkey-patch put into `app/config/initializers/active_admin.rb` does the trick:

```ruby
module ActiveAdmin
  module Views
    module Pages
      class Index
        def main_content
          wrap_with_batch_action_form do
            build_table_tools
            build_collection
            build_table_tools
          end
        end
      end
    end
  end
end
```

`e.preventDefault()` is needed to prevent browser's default behavior when clicking on link with `href='#'` - it scrolls to the top
Merge pull request #2838 from AndreyChernyh/f/multi-batch-buttons

Allow to duplicate 'Batch Actions' button at the bottom
Just a small addition, so now we can remuve multiple filters inline
added unit test
Add better loking template for registrations#new view for admin users. Locale for English and Polish is added.
Merge pull request #2852 from avelexvi/2835-exclude-specific-filters

Just a small addition, so now we can remove multiple filters inline
Merge pull request #2855 from krzysztofbialek/#2790

Properly styled registrations#new template for admin users
Revert "make CSV downloads respect pagination"

This reverts commit a8ad4f989caec3a9ffbc820a949f309d2ce1a832.

Ref: #2847
Merge pull request #2627 from shekibobo/fix-multiline-header

Fix line-collision on wrapped header titles
Merge pull request #2778 from WilliamZang/master

batch actions allow add a proc to form parameter.
updates to #2778
add 'equals' to the filter predicates that default to string

as discovered by @JakeAustwick in IRC:

https://botbot.me/freenode/activeadmin/msg/9660435/
refactor tests for string filters w/ a predicate (e.g. body_equals)
lock Travis icon in README to the master branch
Add ability to order by hstore columns in PostgreSQL

Example:

```ruby
class Device < ActiveRecord::Base
  store_accessor :information, :model
end
```

```ruby
ActiveAdmin.register Device do
  index do
    column :model, sortable: "information->'model'"
  end
end
```
Merge pull request #2844 from AndreyChernyh/f/add-hstore-sort

Add ability to order by hstore columns in PostgreSQL
#2414: don't accidentally set up AA routes multiple times
Support scopes with spaces in the name
clarify the state of the project in the README