Edit a feature, er, feature

@danmaclean this PR adds a cucumber feature to test editing a genome feature.

It's also simplified the logic for the +/- on the radio buttons on the edit page from:
```
<div class="edit_form_elements"><%= f.label "Strand" %></div>
<% if @feature.strand == '+'%>
<%= label_tag(:strand_plus, "+") %>
<input checked="checked" id="strand_plus" name="feature[strand]" type="radio" value="plus" />
<%= label_tag(:strand_minus, "-") %>    
<input id="strand_minus" name="feature[strand]" type="radio" value="minus" />
<% else %>
<%= label_tag(:strand_plus, "+") %>
<input id="strand_plus" name="feature[strand]" type="radio" value="plus" />
<%= label_tag(:strand_minus, "-") %>    
<input checked="checked" id="strand_minus" name="feature[strand]" type="radio" value="minus" />
<% end %>
```
to:
```
  <%= f.input :strand, as: :radio_buttons, collection: ["+", "-" ], item_wrapper_class: "inline" %>
```
which is much cleaner.