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

xs/src/slic3r/GUI/Field.cpp

@@ -586,6 +586,8 @@ boost::any& Choice::get_value()
 			m_value = static_cast<SupportMaterialPattern>(ret_enum);
 		else if (m_opt_id.compare("seam_position") == 0)
 			m_value = static_cast<SeamPosition>(ret_enum);
+		else if (m_opt_id.compare("host_type") == 0)
+			m_value = static_cast<PrintHostType>(ret_enum);
 	}	
 
 	return m_value;