ActiveAdmin::Resource loads resources for breadcrumbs

Closes #2266

Add `ActiveAdmin::Resource#find_resource`. This is now a centralized place to
load a resource, with correct handling of primary key, decoration, etc.

Then, use this new way of loading resources in the Breadcrumbs logic.
This was the original impetus for for defining
`ActiveAdmin::Resource#find_resource`. Previously, the `BreadcrumbsHelper`
did a one-off load of the resource, which has historically been a source of
bugs and/or inconsistencies.

Please note that this is duplication with InheritedResources. Normally, the
resource is loaded by InheritedResources, but there are situations in which
ActiveAdmin needs to load resources as well (ie Breadcrumbs). It was not
reasonable to use InheritedResources to load the resource (see the discussion
at https://github.com/gregbell/active_admin/pull/2315).
Merge pull request #2315 from carnesmedia/config_loads_resource

ActiveAdmin::Resource loads a resource for breadcrumbs
add skip_filter to config
Prevent panels from escaping HTML safe titles

Panels concatinate a non-html_safe, empty string with the title provided. The
resulting new string is always considered unsafe and prevents titles with
HTML from being rendered. This fixes the issue by starting with a html_safe
empty string.
Merge pull request #2403 from zorab47/allow-panel-titles-marked-html-safe

Prevent panels from escaping HTML safe titles
move store configuration into test template file
update #2395 to protect against no user config existing

closes #2399
Merge pull request #2402 from evanwhalen/skip_filter

add skip_filter to config
update the README
fill missing japanese translations. (#2415)
Raise Error when install with ActiveAdminUser as user

Currently installing active admin with 'ActiveAdminUser' fails with
StackLevelTooDeep after login due to a collision of the
current_user_method with the internally used current_active_admin_user.
Merge pull request #2417 from 500tech/reserved-user-names

Raise Error when install with ActiveAdminUser as user
make CSV downloads respect pagination
update select filter to respect custom search methods
resource lookup should also search against resource_name
added spec for resource lookup by string name
Merge pull request #2422 from musicglue/resource_lookup_by_name

ResourceCollection lookup should also search against resource_name
added failing specs for form#title
corrected form#title so it checks for a page title
Merge pull request #2428 from alex-handley/1762-fixed-page-title-for-forms

#1762 fixed page title for forms