Switch gadgets/motd-variations to pure PHP

Summary:
This gadget was a proof of concept calling a TCL script,
but has been committed as is.

This change rewrites the TCL call in pure PHP.
It requires jive and valspeak as executables.

Reformat code to allow the HTML format to be prepended by spaces
and avoid too often to supersede 80 chars.

Ref T1294

Test Plan: Live at https://tools.nasqueron.org/gadgets/motd-variations

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1294

Differential Revision: https://devcentral.nasqueron.org/D1173