set missing Registry keys on windows

[Simon-Laux]

We need some special registry keys for windows to register for the mailto scheme and that users can select Deltachat as default email app.

Also for the other uri schemes, like secure join I guess.

We probably should do this in the installer, which we likely need to look at doing ourselves anyway to be able to finally fix #1269

[Simon-Laux]

for startup tasks we could also use: https://github.com/felixrieseberg/electron-winstore-auto-launch (edit this is appx only)

[Simon-Laux]

this mostly affects the nsis installer, the appx version already registers the mailto scheme properly and is displayed as option for default mail program.

[Simon-Laux]

I made a new issue to track the mailto issue more specifically: #3481

the other registry things should get dedicated issues.

Registration as default handler for dc schemes done at runtime via app.setAsDefaultProtocolClient in

deltachat-desktop/src/main/open_url.ts

Lines 14 to 19 in fd1f8ce

	app.setAsDefaultProtocolClient('openpgp4fpr')
	app.setAsDefaultProtocolClient('OPENPGP4FPR')
	app.setAsDefaultProtocolClient('dcaccount')
	app.setAsDefaultProtocolClient('DCACCOUNT')
	app.setAsDefaultProtocolClient('dclogin')
	app.setAsDefaultProtocolClient('DCLOGIN')