A status document should convey that a user passphrase has been changed

[llemeurfr]

This is the continuation of readium/readium-lcp-server#174, which will not be implemented in the LCP Server v1.

We should create a new private route which sets to now() the date of last update of every license associated with the user who's ID is given as a parameter.

The Provider CMS will be able to call this command after a user has updated his passphrase.

After such command, a fresh license will be fetched the next time the user opens one of his ebooks. This fresh license will include the new text hint and force the entry of the new passphrase.