Tinker_15.07

• separate submenu for preferences
• temperature control for the buildplate is switchable between PID and "bang-bang" mode
• additional setting: less intrusive encoder click
• display effective printing time during cooldown
• bugfix: correct end of print retraction after pause and subsequently abort
• experimental: new expert function "Recover print" - start printing at a selectable height. It works, but parsing the gcode file may take some time (depending on the filesize)