Debug: log mode, allow to skip boot messages

[mcspr]

• Small optimisation for boot speed skipping log completely when booting.
  ENABLED / DISABLED / SKIP_BOOT modes.
  Can be log level / tag / whatever, need more extensive change for that.
  See: https://gitter.im/tinkerman-cat/espurna?at=5e206b6d0dbd9379ed470747
• Fixup yield in the _debugSend() always triggering when either WS or TELNET logging is enabled.
• Fixup issues with Debug: store boot log #2109 & Refactor get/set/del/hasSetting #2048 debugSetup only using defaults from definitions as configuration
• Fix small issue with DEBUG_SUPPORT negative case, preprocessor needs brackets (and would not even issue a warning without them... since ! in the beginning would apply to DEBUG_SERIAL_SUPPORT value)
• Somewhat reworked telnet / debug files, moved things around that make sense to be externalized. Add telnet.h, reference telnet.h and ws.h from debug module. Move telnet debug writer to telnet module.