Occasionally save window/split/tab layout

The window layout is only saved if something has been changed.
When something relevant to the window layout is changed, a save is
queued to run after 10 seconds.
If within those 10 seconds, another thing is changed, that timer is
reset and will run after 10 seconds again.

Events that cause the save to be queued up:
 - Tab created
 - Tab removed
 - Tab moved
 - Tab name changed
 - Split created
 - Split removed
 - Split moved
 - Split channel changed
 - Split resized
 - Window moved
 - Window resized

What currently does not trigger the save to be queued up:
 - Active tab changed

src/widgets/Notebook.cpp

@@ -45,6 +45,9 @@ Notebook::Notebook(QWidget *parent)
 
 NotebookTab *Notebook::addPage(QWidget *page, QString title, bool select)
 {
+    // Queue up save because: Tab added
+    getApp()->windows->queueSave();
+
     auto *tab = new NotebookTab(this);
     tab->page = page;
 
@@ -72,6 +75,9 @@ NotebookTab *Notebook::addPage(QWidget *page, QString title, bool select)
 
 void Notebook::removePage(QWidget *page)
 {
+    // Queue up save because: Tab removed
+    getApp()->windows->queueSave();
+
     for (int i = 0; i < this->items_.count(); i++) {
         if (this->items_[i].page == page) {
             if (this->items_.count() == 1) {
@@ -267,6 +273,9 @@ QWidget *Notebook::tabAt(QPoint point, int &index, int maxWidth)
 
 void Notebook::rearrangePage(QWidget *page, int index)
 {
+    // Queue up save because: Tab rearranged
+    getApp()->windows->queueSave();
+
     this->items_.move(this->indexOf(page), index);
 
     this->performLayout(true);