Refresh the dock's counter field when the numbering actually advances

Reported by @scorpio810 on #626: "The field does not update automatically;
you need to list the other rules for it to update."

Two reasons, both mine:

The refresh was wired to the combo boxes' activated() signal, which Qt
emits only for user interaction. Nothing that changed a context
programmatically -- which is to say, numbering an element -- ever reached
it. Re-picking a rule from the combo was not a workaround so much as the
only code path that refreshed at all.

And there was no signal to hang it on for two of the three categories:
addElementAutoNum() emitted elementAutoNumAdded(), but addConductorAutoNum()
and addFolioAutoNum() emitted nothing, so even a listener would not have
heard a conductor counter advance.

Add QETProject::autoNumContextUpdated(), emitted by all three setters, and
have the dock re-read its three fields on it. Kept deliberately separate
from the existing *AutoNumAdded/*Removed signals: those make listeners
rebuild their rule lists, which is both heavier than needed here and would
disturb the user's current selection every time an element is numbered.
This one only says "re-read me".

The automatic refresh skips a field that has keyboard focus, so numbering
an element cannot overwrite a value half-typed under the cursor. Explicit
refreshes after a reset or an edit still write unconditionally, so the
field always ends up showing the canonical stored value.

Measured, advancing a counter the way numbering advances it and without
touching the combo box:

  field before advance   "5"
  context after advance   6
  field after advance    "6"      (was still "5")

sources/qetproject.cpp

@@ -726,6 +726,7 @@ QHash <QString, NumerotationContext> QETProject::folioAutoNum() const
 */
 void QETProject::addConductorAutoNum(const QString& key, const NumerotationContext& context) {
 	m_conductor_autonum.insert(key, context);
+	emit autoNumContextUpdated();
 }
 
 /**
@@ -739,6 +740,7 @@ void QETProject::addElementAutoNum(const QString& key, const NumerotationContext
 {
 	m_element_autonum.insert(key, context);
 	emit elementAutoNumAdded(key);
+	emit autoNumContextUpdated();
 }
 
 /**
@@ -750,6 +752,7 @@ void QETProject::addElementAutoNum(const QString& key, const NumerotationContext
 */
 void QETProject::addFolioAutoNum(const QString& key, const NumerotationContext& context) {
 	m_folio_autonum.insert(key, context);
+	emit autoNumContextUpdated();
 }
 
 /**