Downloader feature - Downloads from Printables.com

Custom URL Registration:
 - Windows - writes to registers.
 - Linux - desktop integration file.
 - Macos - info.plist.in creates registration and is controlled only via app config.
Registration is first made in Config Wizard. Or is triggered from Preferences. Path to downloads folder can be set.
URL link starts new instance of PS which sends data to running instance via SingleInstance structures if exists.
New progress notification is introduced with pause and stop buttons.
Downloader writes downloaded data by chunks.
Support for zip files is introduced. Zip files can be opened, downloaded or drag'n'droped in PS. Archive dialog is opened. Then if more than 1 project is selected, only geometry is loaded.
Opening of 3mf project now supports openning project in new PS instance.

src/libslic3r/PrintConfig.cpp

@@ -4632,6 +4632,10 @@ CLITransformConfigDef::CLITransformConfigDef()
     def->label = L("Scale to Fit");
     def->tooltip = L("Scale to fit the given volume.");
     def->set_default_value(new ConfigOptionPoint3(Vec3d(0,0,0)));
+
+    def = this->add("delete-after-load", coString);
+    def->label = L("Delete files after loading");
+    def->tooltip = L("Delete files after loading.");
 }
 
 CLIMiscConfigDef::CLIMiscConfigDef()