mu: rename --my-address into --personal-address

This makes things a bit more uniform with all the places where we use
"personal".

--my-address remains as an alias for the command-line option.

Add unit test.

Resolves #2806.

mu/mu-options.hh

@@ -188,7 +188,7 @@ struct Options {
 	 */
 	struct Init {
 		std::string	maildir;		/**< where the mails are */
-		StringVec	my_addresses;		/**< personal e-mail addresses */
+		StringVec	personal_addresses;	/**< personal e-mail addresses */
 		StringVec	ignored_addresses;	/**< addresses to be ignored for
 							 * the contacts-cache */
 		OptSize		max_msg_size;		/**< max size for message files */