Remove common_currency model entirely

- A lot of views / pages / etc needed to be updated too
- Now uses django-money fields entirely
- Create a manual rate exchange backend (needs more work!)

InvenTree/part/templates/part/sale_prices.html

@@ -10,7 +10,9 @@
 <hr>
 
 <div id='price-break-toolbar' class='btn-group'>
-    <button class='btn btn-primary' id='new-price-break' type='button'>{% trans "Add Price Break" %}</button>
+    <button class='btn btn-primary' id='new-price-break' type='button'>
+        <span class='fas fa-plus-circle'></span> {% trans "Add Price Break" %}
+    </button>
 </div>
 
 <table class='table table-striped table-condensed' id='price-break-table' data-toolbar='#price-break-toolbar'>
@@ -81,18 +83,11 @@ $('#price-break-table').inventreeTable({
             sortable: true,
         },
         {
-            field: 'cost',
+            field: 'price',
             title: '{% trans "Price" %}',
             sortable: true,
             formatter: function(value, row, index) {
-                var html = '';
-
-                html += row.symbol || '';
-                html += value;
-
-                if (row.suffix) {
-                    html += ' ' + row.suffix || '';
-                }
+                var html = value;
 
                 html += `<div class='btn-group float-right' role='group'>`