JSHint's ES6 support is shaky, and its development has stalled as of late.
Since ESLint can do by itself both JSHint and JSCS' jobs, this commit replaces them.
Gulp and its related dependencies are also hereby removed.
ResourceMonitor has been moved from app.js into monitor.js and
renamed to simply Monitor. It also gains the ability to fine-
grained control the log level, although in a pretty crude way.
Monitor.debug - bugs in PS's engine that we need to fix
someday - by default, these aren't reported
Monitor.warn - issues that suggest an attacker or poorly
coded custom client - these should probably be looked at
Monitor.notice - issues that staff probably want to know.
These are usually also written to the Staff room.
