ui, logic: design for license ui and forcing the user to enter a key on first open

This change integrates the license key ui into the application and makes it necessary for the user to enter a correct
key. The check for a correct key is done on startup and whenever a project is loaded. The check for the key also
includes a check whether the location of the application has changed.

bin/app/data/gui/license/license.css

@@ -0,0 +1,17 @@
+#licenseField {
+	font-family: "<setting:font_name>";
+	font-size: 12pt;
+	height: 200px;
+	padding: 5px;
+	width: 470px;
+}
+
+#licenseError {
+	color: red;
+}
+
+QTextEdit {
+	background-color: rgba(255, 255, 255, 200);
+	border-radius: 10px;
+	border: 1px solid lightgrey;
+}