logic: background indexing (issue #175)

* allow hiding of indexing dialogs to browse loaded project while indexing
* show indexing status in status bar while indexing
* use different dialog views for different use cases to avoid state collisions
* fixed error label in status bar jittering while indexing
* show hand cursors for clickable elements in status bar
* indexing is not interrupted on pressing ESC while in hidden
* disable error table and error label while indexing
* refactored indexing messages
* forbid indexing and changing project while indexing
* don't show indexing status messages in status bar when indexing in the background
* allow tasks to run in the background

fortune cookie message = A journey is waiting for you.

bin/app/data/gui/tabbed_view/tabbed_view.css

@@ -50,6 +50,10 @@ QTableView {
 	font-size: <setting:font_size>px;
 }
 
+QTableView:disabled {
+	color: <color:table/text/disabled>;
+}
+
 QTableView::item {
 	border-left: 1px solid <color:table/table>;
 }
@@ -92,6 +96,10 @@ QHeaderView::section:vertical {
 	padding: 2px 5px 1px;
 }
 
+QHeaderView::section:disabled {
+	color: <color:table/text/disabled>;
+}
+
 QTableView QTableCornerButton::section {
 	background-color: <color:table/background>;
 	border-bottom: 1px solid <color:table/table>;
@@ -103,6 +111,14 @@ QCheckBox {
 	font-size: <setting:font_size>px;
 }
 
+QLabel {
+	color: <color:table/text/normal>;
+}
+
+QLabel:disabled {
+	color: <color:table/text/disabled>;
+}
+
 #help_button {
 	background: transparent;
 	border: none;