mongodb: not working with PHP 7

[dpocock]

The MongoDB API appears to have changed in PHP 7.

This means the MongoDB code in LogAnalyzer needs to be updated

Here is the new API doc:
http://php.net/manual/en/mongodb.tutorial.library.php

The new MongoDB module appears to be available in Debian stretch (the upcoming release) and it would be nice if the LogAnalyzer MongoDB driver would work with that.