examples: Make possible to select the finger to enroll/verify

Move some common functions to an utilities file.

examples/utilities.h

@@ -0,0 +1,27 @@
+/*
+ * Trivial storage driver for example programs
+ *
+ * Copyright (C) 2019 Marco Trevisan <marco.trevisan@canonical.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef __UTILITIES_H
+#define __UTILITIES_H
+
+FpFinger finger_chooser (void);
+const char * finger_to_string (FpFinger finger);
+
+#endif /* __UTILITIES_H */