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Fixes #476

If a Key Transport message is not encryped for us, don't show a warning.

Key Transport messages are sent for example to repair sessions with specific devices
and are generally not encrypted fo all known devices.

Setting the character count to 0 will disable color notification.
Removes setting for counter toggle.

This was a problem on Windows

- Use libsoup for HTTP operations
- Add new config dialog
- Move code into smaller modules

- Use Gajim FileTransferProgress Dialog
- Use libsoup
- Fixes #467, #419

- Much simpler code
- New config dialog