- Added to main menu possibility to export and import all application date.

- Improved encryption/decryption of exported/imported data.  If accounts
  were exported, they need to be exported again.
- Lots of other implemetation improvements.

app/src/main/kotlin/com/tutpro/baresip/ContactActivity.kt

@@ -119,7 +119,7 @@ class ContactActivity : AppCompatActivity() {
                 }
 
                 Contact.contacts().sortBy { Contact -> Contact.name }
-                ContactsActivity.saveContacts(applicationContext.filesDir, "contacts")
+                Contact.save()
 
                 i.putExtra("name", newName)
                 setResult(Activity.RESULT_OK, i)