API spec doesn't define the search query parameter

Add query parameter "query" that is used to specify the actual search query. Without this it's not obvious how to search for a particular email.

docs/APIv2/swagger-2.0.yaml

@@ -103,6 +103,12 @@ paths:
           required: true
           type: string
           enum: [ from, to, containing ]
+        -
+          name: query
+          in: query
+          description: Search parameter
+          required: true
+          type: string
         -
           name: start
           in: query
@@ -183,4 +189,4 @@ paths:
                       format: int64
                     created:
                       type: string
-                      format: date-time
+                      format: date-time