Pause function

Add a Pause function for jobs.
*Add Pause/Continue Button (webserver side)
*Process Pause/Continue action

Allow the user to pause a job, and continue it later. The user can, for example, be away from the printer or just change the PLA/check the heater etc...

See commit details for more information :) (What works, what need to be check more carefully, and what is okay.)

Contact me for information, feedback etc..