improve the document
move things around

+ moved the spec into the view_helpers folder
+ moved the `display_name` method to the top of the file
exclude association methods from `display_name` helper
Merge pull request #2119 from guangnan/master

Fix inconsistent vocabulary in the docs
Merge pull request #2147 from Daxter/bugfix/2052-exclude-associations-from-display-name-methods

[2052] Exclude associations from display name helper
Closes #2052
get auth specs running
Update the Bulgarian translation (locale :bg)
Merge pull request #2150 from mitio/bulgarian-locale

Update the Bulgarian translation (locale :bg)
Added missing translations to da.yml
Merge pull request #2154 from jokklan/patch-1

Added missing translations to da.yml
get dropdowns working for HABTM

+ `_id` is no longer required when defining associated filters

Assuming Foo HABTM Bars, the below now works as you'd expect:
```ruby
ActiveAdmin.register Foo do
  filter :bars
end
```