Simplify part model

- Remove 'varian't or ''revision' field
- Part name must be unique across database

InvenTree/part/templates/part/detail.html

@@ -42,12 +42,6 @@
             <td>{{ part.IPN }}</td>
         </tr>
         {% endif %}
-        {% if part.variant %}
-        <tr>
-            <td><b>Variant</b></td>
-            <td>{{ part.variant }}</td>
-        </tr>
-        {% endif %}
         <tr>
             <td><b>Description</b></td>
             <td>{{ part.description }}</td>

InvenTree/part/templates/part/part_base.html

@@ -38,9 +38,6 @@
         <h4>
             {{ part.full_name }}
         </h4>   
-        {% if part.variant %}
-        <p>Variant: {{ part.variant }}</p>
-        {% endif %}
         <p><i>{{ part.description }}</i></p>
         <p>
             <div class='btn-group'>