[3.3] Replacing RandomLib

[GwendolenLynch]

In an effort to get PHP 7.1 a happening thing, and per RFC #5893 … removal of RandomLib use in core.

This PR maintains a service under $app['randomgenerator'] for BC.

There is a corner-case BC break with this PR, where someone is type hinting on the service itself, which would be pretty rare.

Imports

use RandomLib\Generator;

to:

use Bolt\Security\Random\Generator;

Function signatures

In the case of a fully namespaced function hint:

function foo(\RandomLib\Generator $generator)
{
}

to

use Bolt\Security\Random\Generator;

// …

function foo(Generator $generator)
{
}

Would generally suffice.

[bobdenotter]

Looks good to me!