Modify webview zip file download to support Github hosted file structure.

[13rac1]

Here's the RW-generic webview release: https://github.com/roundware/roundware-app-webview/releases

The original webview zip files stored listen.html and speak.html in the zip root. When github packages the files for a release it stores everything in a directory as the same name as the zip file itself. The Android code needs to be updated to support both file structures.

/listen.html
/speak.html

vs

/roundware-app-webview-1.0/listen.html
/roundware-app-webview-1.0/speak.html