Run shell on the Flatpak host

When Terminal is running on Flatpak we need to access the host
system, otherwise the app is pretty useless.

Closes: #36

src/lib/Session.cpp

@@ -35,6 +35,7 @@
 #include <QDir>
 #include <QFile>
 #include <QRegExp>
+#include <QStandardPaths>
 #include <QStringList>
 #include <QFile>
 #include <QtDebug>
@@ -324,6 +325,12 @@ void Session::run()
     _shellProcess->setFlowControlEnabled(_flowControl);
     _shellProcess->setErase(_emulation->eraseChar());
 
+    // If we are running on Flatpak, we should have access to the host
+    if (!QStandardPaths::locate(QStandardPaths::RuntimeLocation, QLatin1String("flatpak-info")).isEmpty()) {
+        arguments.prepend(exec);
+        exec = QLatin1String("/usr/bin/flatpak-spawn");
+    }
+
     // this is not strictly accurate use of the COLORFGBG variable.  This does not
     // tell the terminal exactly which colors are being used, but instead approximates
     // the color scheme as "black on white" or "white on black" depending on whether