logic: Added indexing mode to reindex incomplete files (issue #493, #496)

* added radio buttons to start indexing dialog
* don't block task scheduler thread while start indexing dialog is visible
* don't force whole project refresh on settings change
* added help button to start indexing dialog explaining indexing modes
* disable unavailable modes when project needs full refresh
* improved label texts on indexing dialogs
* added --incomplete flag to index command of commandline API
* fixed deletion of window stack elements

bin/app/data/gui/indexing_dialog/indexing_dialog.css

@@ -1,4 +1,4 @@
-QLabel, QCheckBox {
+QLabel, QCheckBox, QRadioButton {
 	color: white;
 }
 
@@ -24,6 +24,15 @@ QLabel, QCheckBox {
 	font-weight: bold;
 }
 
+#option {
+	font-size: 14px;
+	margin-left: 15px;
+}
+
+#option:disabled {
+	color: #A0FFFFFF;
+}
+
 #filePath {
 	font-size: 11px;
 }