Update PostProcessingPlugin.py

[GregValiant]

Add post processor settings to the end of the gcode

Description

If any post processors are active - this change adds text section to the end of the Gcode section in the form:
M104 S0
;End of Gcode
;...Post Processor Settings (all settings)
;[ChangeAtZ]
; caz_enabled = True
; a_trigger = layer_no
; b_targetZ = 5.0
; b_targetL = 10
; c_behavior = keep_value
; caz_output_to_display = False
; e1_Change_speed = True
etcetera, etcetera
; caz_change_retractfeedrate = False
; caz_retractfeedrate = 40
; caz_change_retractlength = False
; caz_retractlength = 6
;SETTING_3 {"global_quality": "[general]\nversion = 4\nname = GV PLA 50\ndefi

Type of change

• [ x] New feature (non-breaking change which adds functionality)

• [ x] My code sucks.
• [ x] I have read the Contribution guide
• I have commented my code, particularly in hard-to-understand areas
• [ x] I have uploaded any files required to test this change