Allow setting rescan interval to 0 (fixes #856)

gui/index.html

@@ -466,9 +466,9 @@
                 </div>
                 <div class="form-group" ng-class="{'has-error': folderEditor.rescanIntervalS.$invalid && folderEditor.rescanIntervalS.$dirty}">
                   <label for="rescanIntervalS"><span translate>Rescan Interval</span> (s)</label>
-                  <input name="rescanIntervalS" id="rescanIntervalS" class="form-control" type="number" ng-model="currentFolder.RescanIntervalS" required min="5"></input>
+                  <input name="rescanIntervalS" id="rescanIntervalS" class="form-control" type="number" ng-model="currentFolder.RescanIntervalS" required min="0"></input>
                   <p class="help-block">
-                    <span translate ng-if="!folderEditor.rescanIntervalS.$valid && folderEditor.rescanIntervalS.$dirty">The rescan interval must be at least 5 seconds.</span>
+                    <span translate ng-if="!folderEditor.rescanIntervalS.$valid && folderEditor.rescanIntervalS.$dirty">The rescan interval must be a non-negative number of seconds.</span>
                   </p>
                 </div>
               </div>