Fix typo in define name, preventing printing of bulk send errors
Allow redirecting and disabling log output at runtime

Previously, a few defines in GSCore.h defined all aspects of logging,
and logging always happend to SERIAL_PORT_MONITOR. Now, these constants
still define what is logged exactly, but logging is divided into error
and debug messages, both of which can be redirected or disabled at
runtime. By default, regular errors and line dumps are selected, but
disabled.

Additionally, the defines have been replaced by regular bool constants,
which allows putting them inside regular if() statements, making the
code shorter (not requiring both an if and a #if).