keys with unicode

Using JavaFileKache.
I found that if one of the keys has a unicode char, when the kache is closed and opened again, it is cleared.

As a workaround, I'm now encoding the key to hex:
`key = originalKey.toByteArray().toHexString()
`

And since I also neeed to get the original text for kache managing, I use:
`originalKey = key.hexToByteArray().decodeToString()
`
