Add screenshot generator for themes (and screenshots themselves)

Gemfile.lock

@@ -7,9 +7,16 @@ GEM
       minitest (~> 5.1)
       thread_safe (~> 0.1)
       tzinfo (~> 1.1)
+    capybara (2.4.4)
+      mime-types (>= 1.16)
+      nokogiri (>= 1.3.3)
+      rack (>= 1.0.0)
+      rack-test (>= 0.5.4)
+      xpath (~> 2.0)
     celluloid (0.16.0)
       timers (~> 4.0.0)
     chunky_png (1.3.4)
+    cliver (0.3.2)
     coderay (1.1.0)
     coffee-script (2.3.0)
       coffee-script-source
@@ -89,17 +96,27 @@ GEM
       sprockets (~> 2.12.1)
       sprockets-helpers (~> 1.1.0)
       sprockets-sass (~> 1.3.0)
+    mime-types (2.4.3)
+    mini_magick (4.1.0)
+    mini_portile (0.6.2)
     minitest (5.5.1)
     multi_json (1.11.0)
     net-sftp (2.1.2)
       net-ssh (>= 2.6.5)
     net-ssh (2.9.2)
+    nokogiri (1.6.6.2)
+      mini_portile (~> 0.6.0)
     padrino-helpers (0.12.5)
       i18n (~> 0.6, >= 0.6.7)
       padrino-support (= 0.12.5)
       tilt (~> 1.4.1)
     padrino-support (0.12.5)
       activesupport (>= 3.1)
+    poltergeist (1.6.0)
+      capybara (~> 2.1)
+      cliver (~> 0.3.1)
+      multi_json (~> 1.0)
+      websocket-driver (>= 0.2.0)
     pry (0.10.1)
       coderay (~> 1.1.0)
       method_source (~> 0.8.1)
@@ -136,14 +153,22 @@ GEM
     uglifier (2.7.1)
       execjs (>= 0.3.0)
       json (>= 1.8.0)
+    websocket-driver (0.5.3)
+      websocket-extensions (>= 0.1.0)
+    websocket-extensions (0.1.2)
+    xpath (2.0.0)
+      nokogiri (~> 1.3)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
+  capybara
   middleman (~> 3.3.10)
   middleman-deploy (~> 1.0)
   middleman-livereload (~> 3.1.0)
   middleman-pry (~> 0.0.4)
+  mini_magick
+  poltergeist
   tzinfo-data
   wdm (~> 0.1.0)