Adding Sidekiq for background processing (firstly just of mailers)

Gemfile.lock

@@ -60,6 +60,7 @@ GEM
       execjs
     coffee-script-source (1.10.0)
     concurrent-ruby (1.0.1)
+    connection_pool (2.2.0)
     crack (0.4.3)
       safe_yaml (~> 1.0.0)
     debug_inspector (0.0.2)
@@ -188,6 +189,8 @@ GEM
       rack
     rack-mini-profiler (0.9.9.2)
       rack (>= 1.2.0)
+    rack-protection (1.5.3)
+      rack
     rack-test (0.6.3)
       rack (>= 1.0)
     rails (4.2.5.2)
@@ -271,6 +274,10 @@ GEM
       json (~> 1.7, >= 1.7.7)
       rdoc (~> 4.0)
     sexp_processor (4.7.0)
+    sidekiq (4.1.1)
+      concurrent-ruby (~> 1.0)
+      connection_pool (~> 2.2, >= 2.2.0)
+      redis (~> 3.2, >= 3.2.1)
     simple_form (3.2.1)
       actionpack (> 4, < 5.1)
       activemodel (> 4, < 5.1)
@@ -279,6 +286,10 @@ GEM
       json (~> 1.8)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.0)
+    sinatra (1.4.7)
+      rack (~> 1.5)
+      rack-protection (~> 1.4)
+      tilt (>= 1.3, < 3)
     slop (3.6.0)
     sprockets (3.5.2)
       concurrent-ruby (~> 1.0)
@@ -362,8 +373,10 @@ DEPENDENCIES
   rubocop
   sass-rails (~> 5.0)
   sdoc (~> 0.4.0)
+  sidekiq
   simple_form
   simplecov
+  sinatra
   therubyracer
   turbolinks (~> 5.0.0.beta)
   uglifier (>= 1.3.0)