Common 'console' methods

Add some frequently-used methods from the traditional browser 'console' object to the methods of the BBS's console object as well as (a new) JSexec console object. Methods to consider:

console.assert() - tricky
console.debug()
console.error()
console.info()
console.log()
console.warn()

All but assert() would be basically wrappers for log(level, fmt, ...). In JSexec these would go to stdout by default (or wherever the log output is configured to go) and in the BBS (servers, services) whereever log output normally goes.

This would make more example JavaScript code "just work" in sbbs/JSexec.