set RSBE_* environment variables to nil.

Set RSBE_* environment variables to nil to prevent accidental modification of
  a production service during testing.
add Rsbe::Client::MethodNotImplementedError class
add collection vcr cassettes
add Rsbe::Client::Collection class
clean up

Clean up "NotFound" error message.
Clean up nesting in not_found_error.rb file.
add Base#get_children
add Partner#get_collections
Merge pull request #16 from jgpawletko/add-colls

Add Rsbe::Client::Collections