Updated the version from 1.1 to 1.2
Renamed the header to "Slint Royalty-free Desktop, Mobile, and Web Applications License"
Added definition of "Mobile Application" and grant of right
Moved "Limitations" to 3rd section and "License Conditions - Attributions" to 2nd section
Added flexibility to choose between showing "MadeWithSlint" as a dialog/splash screen or on a public webpage
Moved the para on copyright notices to section under "Limitations"
Semi-random selection of clippy topics that were
uncontroversial before:-).
Leaves about 84 deduplicated issues in the code base
according to clippy from nightly.
Add some code to do platform-independent path processing.
This is necessary aas WASM does e.g. not have any absolute paths and
such and the compiler tended to produce wrong results in that case.
Side-effect: We no longer need to depend on `dunce`
