getLocalHtmlUrlFromRemoteUrl
Takes a remote url pointing to zip file assets and then downloads them into a local directory.
The local content folder will be created one level under localDirectory and the assets from remoteZipUrl will be unzipped into that location. Finally, this method will return the local URL pointing to the assets using the "file://" protocol.
We clear the cache directory before any downloads in case orphaned in-app messages exist on the system.
In case of error, any files created will be deleted. This includes any files downloaded or unzipped.
Return
the local web content directory on the file system. Returns null if the download fails.
Parameters
localDirectory
the directory where the assets will be downloaded
remoteZipUrl
the URL for the assets zip