Move EE specific code out of the Project model

This moves various EE specific lines from the Project model into the
EE::Project module. As a result of these changes, the only EE specific
line is now the `prepend` call to inject the `EE::Project` module.

app/models/project.rb

@@ -78,7 +78,6 @@ class Project < ActiveRecord::Base
   default_value_for :wiki_enabled, gitlab_config_features.wiki
   default_value_for :snippets_enabled, gitlab_config_features.snippets
   default_value_for :only_allow_merge_if_all_discussions_are_resolved, false
-  default_value_for :only_mirror_protected_branches, true
 
   add_authentication_token_field :runners_token
 
@@ -140,7 +139,6 @@ class Project < ActiveRecord::Base
   # Project services
   has_one :campfire_service
   has_one :drone_ci_service
-  has_one :gitlab_slack_application_service
   has_one :emails_on_push_service
   has_one :pipelines_email_service
   has_one :irker_service
@@ -547,14 +545,6 @@ class Project < ActiveRecord::Base
       .base_and_ancestors(upto: top)
   end
 
-  def root_namespace
-    if namespace.has_parent?
-      namespace.root_ancestor
-    else
-      namespace
-    end
-  end
-
   def lfs_enabled?
     return namespace.lfs_enabled? if self[:lfs_enabled].nil?
 
@@ -1297,7 +1287,6 @@ class Project < ActiveRecord::Base
 
   # Expires various caches before a project is renamed.
   def expire_caches_before_rename(old_path)
-    # TODO: if we start using UUIDs for cache, we don't need to do this HACK anymore
     repo = Repository.new(old_path, self)
     wiki = Repository.new("#{old_path}.wiki", self)
 

ee/app/models/ee/project.rb

@@ -29,6 +29,7 @@ module EE
       has_one :jenkins_service
       has_one :jenkins_deprecated_service
       has_one :github_service
+      has_one :gitlab_slack_application_service
 
       has_many :approvers, as: :target, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
       has_many :approver_groups, as: :target, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
@@ -91,6 +92,7 @@ module EE
       end
 
       default_value_for :packages_enabled, true
+      default_value_for :only_mirror_protected_branches, true
     end
 
     class_methods do
@@ -560,6 +562,14 @@ module EE
       instance.token
     end
 
+    def root_namespace
+      if namespace.has_parent?
+        namespace.root_ancestor
+      else
+        namespace
+      end
+    end
+
     private
 
     def set_override_pull_mirror_available