Improved delete friend confirmation dialog, added delete chat logs confi...

Modified delete friend dialog to ask for confirmation of deletion and to provide a check box for deleting the logs(related to feature request https://github.com/Astonex/Antox/issues/389):
![delete_user_confirmation_dialog](https://cloud.githubusercontent.com/assets/8239522/4108106/aa78bdea-31d1-11e4-9938-ea868e698625.png)

Added a confirmation dialog when deleting chat logs:
![delete_chat_logs_confirmation_dialog](https://cloud.githubusercontent.com/assets/8239522/4108109/b98c0364-31d1-11e4-8da2-086e8a3c10fd.png)