Remove que_mailer gem

Closes #895

Gemfile

@@ -85,9 +85,6 @@ gem 'uuidtools', '2.1.5' # For unique IDs (used by the epp gem)
 gem 'que',           '0.10.0'
 gem 'daemons-rails', '1.2.1'
 gem 'que-web',       '0.4.0'
-gem 'que_mailer',
-    github: 'prehnRA/que-mailer',
-    branch: 'master'
 
 # for importing legacy db
 gem 'activerecord-import', '0.7.0' # for inserting dummy data

Gemfile.lock

@@ -41,18 +41,6 @@ GIT
       hpricot
       libxml-ruby
 
-GIT
-  remote: https://github.com/prehnRA/que-mailer.git
-  revision: 32156f258993348b50a7db2a41eed1bdb0bf4fab
-  branch: master
-  specs:
-    que_mailer (0.0.2)
-      actionmailer (>= 4.0)
-      activesupport (>= 4.0)
-      pg (~> 0)
-      que (~> 0.6)
-      rails (>= 4.0)
-
 GIT
   remote: https://github.com/tarmotalu/digidoc_client.git
   revision: 1645e83a5a548addce383f75703b0275c5310c32
@@ -497,7 +485,6 @@ DEPENDENCIES
   puma
   que (= 0.10.0)
   que-web (= 0.4.0)
-  que_mailer!
   railroady (= 1.3.0)
   rails (= 4.2.11.1)
   rails-settings-cached (= 0.4.1)