Fix mismatch of shared console log file extension with its content type

### Issue description

Currently, the console contents are shared as a file with the `.txt` file extension when tapping on "..." -> "Share console" in the Tabris.js iOS client, although they have HTML contents.

### Proposed solution

The console contents should be shared as a file with the `.html` extension when tapping on "..." -> "Share console".

### Alternative solutions

Alternatively, the contents of the console logs could be changed to simple plain text, bringing the behavior in line with the Android client.