add min and max attributes to validuntil field

uffd/invite/templates/invite/new.html

@@ -11,7 +11,11 @@
 	</div>
 	<div class="form-group">
 		<label for="valid-until">{{_('Valid Until')}}</label>
-		<input class="form-control" type="datetime-local" id="valid-until" name="valid-until" value="{{ (datetime.now() + timedelta(hours=36)).replace(hour=23, minute=59, second=59, microsecond=0).isoformat(timespec='minutes') }}">
+		<input class="form-control" type="datetime-local" id="valid-until" name="valid-until"
+				value="{{ (datetime.now() + timedelta(hours=36)).replace(hour=23, minute=59, second=59, microsecond=0).isoformat(timespec='minutes') }}"
+				min="{{ (datetime.now() + timedelta(minutes=10)).isoformat(timespec='minutes') }}"
+				max="{{ (datetime.now() + timedelta(days=config['INVITE_MAX_VALID_DAYS'])).isoformat(timespec='minutes') }}"
+		>
 		<small class="text-muted">{{_('Must be within the next %(max_valid_days)d days', max_valid_days=config['INVITE_MAX_VALID_DAYS'])}}</small>
 	</div>
 	{% if allow_signup %}