The design system tokens are specified in the _base.scss file. To avoid to duplicate their value in a rust file, a new
step has been added to the building process to generate the `style_vars.rs` file which make the color tokens reachable
to the app.
- Remove of the flume dependency.
- Add the capability to share data provided by the Matrix client to the ChatsWindow. Indeed, until the 0.6 Dioxus
release, each window runs in a separate virtual DOM so the context and Fermi states are completely seperate
(cf. https://discord.com/channels/899851952891002890/1188206938215948378).
