add @ingroup to all field handlers

Conflicts:

	modules/comment/views_handler_field_comment_link_approve.inc
	modules/node/views_handler_field_history_user_timestamp.inc
	modules/system/views_handler_field_file_filemime.inc
	modules/user/views_handler_field_user_link_cancel.inc
	modules/user/views_handler_field_user_permissions.inc