Prepare support for partial updates

As webdav-client may support it one day. And thus WebDAV-Drive also,
when we manage to implement the upload progress over fetch.

See: perry-mitchell/webdav-client#362, club-1/webdav-drive#65

nginx.conf

@@ -32,15 +32,15 @@ server {
 		if ($request_method = OPTIONS) {
 			# CORS headers for JS frontend
 			add_header access-control-allow-origin *;
-			add_header access-control-allow-methods GET,POST,PUT,DELETE,OPTIONS,PROPFIND,PROPPATCH,MOVE,COPY,MKCOL,LOCK,UNLOCK;
+			add_header access-control-allow-methods GET,POST,PUT,PATCH,DELETE,OPTIONS,PROPFIND,PROPPATCH,MOVE,COPY,MKCOL,LOCK,UNLOCK;
 			add_header access-control-allow-credentials true;
 			add_header access-control-allow-headers authorization,dnt,user-agent,keep-alive,content-type,accept,origin,depth,destination;
 
 			# Tell client that this preflight info is valid for 100h
 			add_header access-control-max-age 360000;
 
 			# DAV header
-			add_header dav 1,2,3,extended-mkcol;
+			add_header dav 1,2,3,extended-mkcol,sabredav-partialupdate;
 
 			# Allways return OK as browsers do not use auth credentials on preflight
 			return 204;