Miscellaneous changes to the Asset DB (#390)

* FIX #388: Prevent assets losing supplier data on edit

* FEAT: Add associated assets to supplier detail view

* FIX: Tweak supplier list to make detail view accessible

* Potential fix for #380

No idea if it works because I can't reproduce locally. S/O Reckons it should... :P

* FEAT #386: Asset search searches serial number.

Pending addition of advanced search.

* FIX: Order asset categories/statuses alphabetically

Instead of by pk because that's silly.

* FEAT: Statuses can have a CSS class defined in the admin panel

This replaces the hardcoding of colours in the asset list.

* FIX: Squash migrations

* Fixed supplier not working on all the create asset template

* Refactored away "assets" property on "Supplier" by using "related_name" instead

Co-authored-by: Matthew Smith <mattysmith22@googlemail.com>

assets/templates/asset_list.html

@@ -11,8 +11,8 @@
 
 <form id="asset-search-form" method="get" class="form-inline pull-right">
   <div class="input-group pull-right" style="width: auto;">
-    {% render_field form.query|add_class:'form-control' placeholder='Search by Asset ID/Description' style="width: 250px"%}
-    <label for="query" class="sr-only">Asset ID/Description:</label>
+    {% render_field form.query|add_class:'form-control' placeholder='Search by Asset ID/Desc/Serial' style="width: 250px"%}
+    <label for="query" class="sr-only">Asset ID/Description/Serial Number:</label>
     <span class="input-group-btn"><button type="submit" class="btn btn-default">Search</button></span>
   </div>
   <br>