Improved support for panelolu2 encoder and buzzer

Added #define for LCD_FEEDBACK_FREQUENCY_HZ and
LCD_FEEDBACK_FREQUENCY_DURATION_MS  which is used to alter the default feedback
buzzer sound.

When selecting Panelolu2 in configuration.h:
- it automatically sets the correct ENCODER_PULSES_PER_STEP and
ENCODER_STEPS_PER_MENU_ITEM.
- if LCD_USE_I2C_BUZZER is defined it will also set the default
LCD_FEEDBACK_FREQUENCY_HZ and LCD_FEEDBACK_FREQUENCY_DURATION_MS

When you now select the sanguinololu 1284p the following happens:
- it enables  LARGE_FLASH
- It enables the gcode M300 when the panelolu2 LCD_USE_I2C_BUZZER is
defined