Add possibility to export/import messages to file

[Carael]

Add possibility to export queue/topic messages to file (with removal or just peeking).

• export body and application properties with cross bus explorer format
• if no cross buss format - just set the body with the file content

Export to multiple files in selected folder.

Import files for selected queue/topic.

[Carael]

The possibility to import messages from file (just body) has been introduced in version 0.4.7.