Not compatible with Leptos 0.7

[mscherer]

There was some pretty big change on Leptos 0.7, including:

• moving lots of things to leptos::prelude
• renaming some API from create_* to * (with some missing, so breaking build)
• rustc throw some compilation errors, as some types now need to be Send and Sync, resulting in having to make ServerSignalEventSource being threadsafe (with EventSource not being thread safe, so I think that just requires to throw some Arc and RWlock in the right place).

See https://github.com/leptos-rs/leptos/releases/tag/v0.7.0

[messense]

Pull requests are welcome!

[justjoheinz]

My Rust know how is unfortunately not good enough yet, but it would be awesome if the library would be upgraded to newer leptos versions.