Merge branch 'improve_empty_fork' into 'master'

Show message if user tries to fork and has no available namespaces

This merge request improves the UX when users try to fork a project and have no eligible namespaces. 

### Current behavior

![Screen_Shot_2015-09-25_at_1.39.45_PM](https://gitlab.com/dblessing/gitlab-ce/uploads/45a303703a0197e78f7f9bdbea8718b5/Screen_Shot_2015-09-25_at_1.39.45_PM.png)

### Proposed behavior

![Screen_Shot_2015-09-25_at_1.38.57_PM](https://gitlab.com/dblessing/gitlab-ce/uploads/613c53bcfb52d79fdf8bd1d09410c152/Screen_Shot_2015-09-25_at_1.38.57_PM.png)

### Things to check

I'm not exactly loving the wording I have here. I'm open to improvements.


See merge request !1441

app/views/projects/forks/new.html.haml

 - page_title "Fork project"
-%h3.page-title Fork project
-%p.lead
+- if @namespaces.present?
+  %h3.page-title Fork project
+  %p.lead
     Click to fork the project to a user or group
-%hr
+  %hr
 
-.fork-namespaces
+  .fork-namespaces
     - @namespaces.in_groups_of(6, false) do |group|
       .row
         - group.each do |namespace|
@@ -31,6 +32,10 @@
       Fork is a copy of a project repository.
       %br
       Forking a repository allows you to do changes without affecting the original project.
+- else
+  %h3 No available namespaces to fork the project
+  %p.slead
+    You must have permission to create a project in a namespace before forking.
 
 .save-project-loader.hide
   .center