Turn application state into enum

The application state was encoded in a QByteArray. Thus, there was
no compile-time checking. Typos would lead to silent failures.

Turn the application state into an enum. Use the enum-class construct,
so that the values don't polute the global namespace. Moreover,
this makes them strongly typed, i.e. they don't auto-convert to
integers.

A disadvantage is that the enums now have to be cast to int
explicitly when used to index an array.

Replace two hash-maps in MainWindow to arrays of fixed sizes.

Move the application-state details into their own files.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/qthelper.cpp

@@ -12,6 +12,7 @@
 #include "divecomputer.h"
 #include "time.h"
 #include "gettextfromc.h"
+#include "applicationstate.h"
 #include "metadata.h"
 #include <sys/time.h>
 #include "exif.h"
@@ -1362,21 +1363,9 @@ extern "C" void parse_display_units(char *line)
 	qDebug() << line;
 }
 
-static QByteArray currentApplicationState;
-
-QByteArray getCurrentAppState()
-{
-	return currentApplicationState;
-}
-
-void setCurrentAppState(const QByteArray &state)
-{
-	currentApplicationState = state;
-}
-
 extern "C" bool in_planner()
 {
-	return currentApplicationState == "PlanDive" || currentApplicationState == "EditPlannedDive";
+	return getAppState() == ApplicationState::PlanDive || getAppState() == ApplicationState::EditPlannedDive;
 }
 
 extern "C" enum deco_mode decoMode()