wasm: accept commandline arguments

emscripten has partial support for passing commandline arguments to the webpage app.

You can pass arguments to wasm apps two ways:

http://localhost:6931/wasm-args.html?files=quark.qml,quack.qml

even easier,  emrun has support

emrun --browser=firefox_nightly wasm-args.html "files=quark.qml&files2=quack.qml"

The glue to have them show up as argv exists in emscripten, but needs javascript glue.