refactored admin controller - use 1 public api action (PageController#action) which decides if a user should be activated, deactivated or deleted via params[:type], added simple mail action and view
renamed mail.erb to mail.html.erb
added admin mail submit action route
updated mail html preview test to check new logic
implemented submit action, implemented mail html preview action partial
added styling for mail html preview
added mail html preview view
use parentheses for minitest assertions
use parentheses for methods with params
use parentheses for minitest assertions with param
set assets host for mailer
AdminController Tests are finished
implemented test for UserMaile#newsletter
use parentheses for methods with params (even rails dsl methods), add newsletter view, use image_tag in mailer views
impelementd UserMailer#newsletter
implemented AdminController#email_preview & AdminController#send_mails
remove legacy app submodule