check that file paths in encryption.xml are treated as URIs

[llemeurfr]

We may encounter spaces and other non-ascii characters in file names.

ex.
<enc:CipherReference URI="images/an%20image.jpeg"/>

The encryption tool had a bug, the path was not % encoded so far. This bug will soon be resolved and we must make sure that this will not create a client side issue.

[qnga]

Should be fixed in Streamer PR readium/r2-lcp-kotlin#89.