Merge branch 'atomaka/refactor/demeter-fixes' into 'master'

Fix some law of demeter violations

```
@post.user.username
```

is not good

```
delegate :username, to: :user, prefix: true
@post.user_username
```

is apparently good? Although I've never really seen the advantage since I feel like we're just masking an underlying problem.  But at least it looks a little nicer.

See merge request !14

app/models/post.rb

@@ -2,6 +2,8 @@ class Post < ActiveRecord::Base
   belongs_to :user
   belongs_to :subcreddit
 
+  delegate :username, to: :user, prefix: true
+
   validates :title,
     presence: true,
     length: { maximum: 300 }

app/models/subcreddit.rb

@@ -8,6 +8,8 @@ class Subcreddit < ActiveRecord::Base
 
   attr_accessor :closed
 
+  delegate :username, to: :owner, prefix: true
+
   before_save :set_closed_at
 
   validates :name,

app/views/application/_sidebar.html.slim

@@ -18,4 +18,4 @@
     .title Moderators
     .box
       ul
-        li= @subcreddit.owner.username
+        li= @subcreddit.owner_username

app/views/posts/show.html.slim

@@ -1,7 +1,7 @@
 .posts
   .post.show
     p.title= link_to @post.title, [@subcreddit, @post]
-    p.details= "submitted #{distance_of_time_in_words @post.created_at, Time.now} ago by #{@post.user.username}"
+    p.details= "submitted #{distance_of_time_in_words @post.created_at, Time.now} ago by #{@post.user_username}"
     ul.links.list-inline
       li= link_to 'XXX comments', ''
       li= link_to 'source', ''

app/views/subcreddits/show.html.slim

@@ -7,7 +7,7 @@
         li
           .post
             p.title= link_to post.title, [@subcreddit, post]
-            p.details= "submitted #{distance_of_time_in_words post.created_at, Time.now} ago by #{post.user.username}"
+            p.details= "submitted #{distance_of_time_in_words post.created_at, Time.now} ago by #{post.user_username}"
             ul.links.list-inline
               li= link_to 'XXX comments', ''
               li= link_to 'share', ''

spec/models/post_spec.rb

@@ -6,6 +6,8 @@ describe Post, type: :model do
   it { should belong_to(:user) }
   it { should belong_to(:subcreddit) }
 
+  it { should delegate_method(:username).to(:user).with_prefix }
+
   context 'with valid data' do
     it 'should be valid' do
       expect(post).to be_valid

spec/models/subcreddit_spec.rb

@@ -7,6 +7,8 @@ describe Subcreddit, type: :model do
 
   it { should belong_to(:owner).class_name('User') }
 
+  it { should delegate_method(:username).to(:owner).with_prefix }
+
   context 'with valid data' do
     it 'should be valid' do
       expect(subcreddit).to be_valid