This PR splits the GUI source files from the core
source files. The immediate goal is to allow the
CLI to require only a minimum number of dynamic
libraries. The long term goal is to create an
architectural boundary around the core module,
in preparation of libkdbx.
Fixes#5001.
The favicon download URL was constructed from scheme and host only. This is fixed by simply replacing the path of the original URL with "/favicon.ico", thus keeping scheme, host, auth and port intact.
Further modification: URL's with a non-http schema are now rejected.