Add vCard support

Only nicknames, photos, birthdays, addresses, telephone numbers, emails,
JIDs, titles, roles, notes, and URLs are supported

Due to the synopsis array not having enough space, `/vcard photo
open-self` and `/vcard photo save-self` are not documented properly in
the synopsis section of the `/vcard` command, but they are documented in
the arguments section

Fixed memory leak in vcard autocomplete (thanks to debXwoody)

src/config/files.h

@@ -60,6 +60,7 @@
 #define DIR_DOWNLOADS "downloads"
 #define DIR_EDITOR    "editor"
 #define DIR_CERTS     "certs"
+#define DIR_PHOTOS    "photos"
 
 void files_create_directories(void);