Allow setting space host in UI

Author: fbacall

app/views/spaces/_form.html.erb

@@ -3,6 +3,8 @@
 
   <%= f.input :title %>
 
+  <%= f.input(:host) if current_user.is_admin? %>
+
   <%= f.input :description, as: :markdown_area, input_html: { rows: '10' } %>
 
   <%= f.input :theme, collection: Space::THEMES, selected: @space.theme || 'default' %>