Create brokerage account model
Define policy for brokerage account resources
Add new routes to handle brokerage account resource
Explicitly define url of brokerage account form

Since brokerage account uses singular resource route, simple_form (nor
Rails' form_tag) does not detect the right url properly.
not detect automatically
Merge pull request #693 from neighborly/im-order

Allow users to fill information about a brokerage account