Abilities refactoring

app/models/ability.rb

@@ -19,7 +19,7 @@ class Ability
       :read_team_member,
       :read_merge_request,
       :read_note
-    ] if project.readers.include?(user)
+    ] if project.allow_read_for?(user)
 
     rules << [
       :write_project,
@@ -27,16 +27,18 @@ class Ability
       :write_snippet,
       :write_merge_request,
       :write_note
-    ] if project.writers.include?(user)
+    ] if project.allow_write_for?(user)
 
     rules << [
+      :modify_issue,
+      :modify_snippet,
       :admin_project,
       :admin_issue,
       :admin_snippet,
       :admin_team_member,
       :admin_merge_request,
       :admin_note
-    ] if project.admins.include?(user)
+    ] if project.allow_admin_for?(user)
 
     rules.flatten
   end
@@ -48,6 +50,7 @@ class Ability
           [
             :"read_#{name}",
             :"write_#{name}",
+            :"modify_#{name}",
             :"admin_#{name}"
           ]
         else