Added possibility for upload to Duet

Further changes:
- Added new configuration option Host Type
- Added abstract base class for future printer hosts
- Moved location of upload dialog (also made it a little bit more configureable)
- added possibility to send file via postfield instead a new frame

resources/profiles/PrusaResearch.ini

@@ -1007,8 +1007,8 @@ max_layer_height = 0.25
 min_layer_height = 0.07
 max_print_height = 200
 nozzle_diameter = 0.4
-octoprint_apikey = 
-octoprint_host = 
+printhost_apikey = 
+print_host = 
 printer_notes = Don't remove the following keywords! These keywords are used in the "compatible printer" condition of the print and filament profiles to link the particular print and filament profiles to this printer profile.\nPRINTER_VENDOR_PRUSA3D\nPRINTER_MODEL_MK2\n
 printer_settings_id = 
 retract_before_travel = 1