Add a browser-utils crate (#4394)

* Squash

* Fix keystore on wasm

* Update utils/browser/Cargo.toml

Co-Authored-By: Benjamin Kampmann <ben@gnunicorn.org>

* export console functions

* Use an Option<PathBuf> in keystore instead of cfg flags

* Add a KeystoreConfig

* Update libp2p

* Bump kvdb-web version

* Fix cli

* Upgrade versions

* Update wasm-bindgen stuff

Co-authored-by: Benjamin Kampmann <ben.kampmann@googlemail.com>

substrate/bin/node/cli/browser-demo/build.sh

@@ -1,3 +1,3 @@
 #!/usr/bin/env sh
 wasm-pack build --target web --out-dir ./browser-demo/pkg --no-typescript --release ./.. -- --no-default-features --features "browser"
-python -m SimpleHTTPServer 8000
+python -m http.server 8000