Add option to print/not-print levelMsg in log out

I was interested in using console++ primarily for the configurable log levels and colors, but would prefer an unmodified console.log. 

This PR adds the ability to disable the `[LEVEL` part of the formatted output, which in conjunction with the disableTimestamp option enables a pure console.log output. 

It's set up so you can mix and match, ie, timestamp, no level, level no timestamp, nothing at all...

Methods added:

`enableLevelMsg()`
`disableLevelMsg()`
`isLevelMsgPrinted()`