Use webpack extract_css: true all of the time (#204)

Webpacker has a nasty habit of not compiling css files for components and then causing an error in production when they are missing.
rails/webpacker#2342
rails/webpacker#2059 (comment)

Unfortunately using extract_css: true all the time apparently comes with some performance impacts, however the tradeoff is the application actually works correctly in development mode.

app/views/projects/index.html.haml

@@ -1,8 +1,7 @@
 - content_for :assets do
   = javascript_pack_tag 'projects'
-  = stylesheet_pack_tag 'projects'
 
 #Projects
   %Projects{                                                   |
     'v-bind:projects': @projects.to_json,                      |
-  }  
+  }

app/views/users/index.html.haml

@@ -1,8 +1,7 @@
 - content_for :assets do
   = javascript_pack_tag 'users'
-  = stylesheet_pack_tag 'users'
 
 #users
   %Users{                           |
     'v-bind:users': @users.to_json, |
-  }  
+  }

config/webpacker.yml

@@ -17,7 +17,7 @@ default: &default
   cache_manifest: false
 
   # Extract and emit a css file
-  extract_css: false
+  extract_css: true
 
   static_assets_extensions:
     - .jpg