Document: Rename DocumentPageResult model

Rename the DocumentPageResult to DocumentPageSearchResult for
clarity of purpose.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/documents/models.py

@@ -971,7 +971,7 @@ class DocumentPage(models.Model):
         return '{}-{}'.format(self.document_version.uuid, self.pk)
 
 
-class DocumentPageResult(DocumentPage):
+class DocumentPageSearchResult(DocumentPage):
     class Meta:
         ordering = ('document_version__document', 'page_number')
         proxy = True