feat: show call participants in room list (Discord-style)

docs/app-load.md

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+# App load order
+
+**Dev note**: As of March 2022, the skin is no longer part of the app load order at all. The document's graphs have
+been kept untouched for posterity.
+
+Old slow flow:
+
+```mermaid
+flowchart TD
+    A1(((load_modernizr))) --> B
+    A2((rageshake)) --> B
+    B(((skin))) --> C
+    C(((olm))) --> D
+    D{mobile} --> E
+    E((config)) --> F
+    F((i18n)) --> G
+    style F stroke:lime
+    G(((theme))) --> H
+    H(((modernizr))) --> app
+    style H stroke:red
+```
+
+Current more parallel flow:
+
+```mermaid
+flowchart TD
+    subgraph index.ts
+        style index.ts stroke:orange
+
+        A[/rageshake/] --> B{mobile}
+        B-- No -->C1(.)
+        B-- Yes -->C2((redirect))
+        C1 --> D[/olm/] --> R
+        C1 --> E[platform] --> F[/config/]
+        F --> G1[/skin/]
+        F --> R
+        G1 --> H
+        G1 --> R
+        F --> G2[/theme/]
+        G2 --> H
+        G2 --> R
+        F --> G3[/i18n/]
+        G3 --> H
+        G3 --> R
+        H{modernizr}-- No --> J((incompatible))-- user ignore --> R
+        H-- Yes --> R
+
+        linkStyle 0,7,9,11,12,14,15 stroke:blue;
+        linkStyle 4,8,10,13,16 stroke:red;
+    end
+
+    R>ready] --> 2A
+    style R stroke:gray
+
+    subgraph init.tsx
+        style init.tsx stroke:lime
+        2A[loadApp] --> 2B[matrixchat]
+    end
+
+```
+
+Key:
+
+- Parallelogram: async/await task
+- Box: sync task
+- Diamond: conditional branch
+- Circle: user interaction
+- Blue arrow: async task is allowed to settle but allowed to fail
+- Red arrow: async task success is asserted
+
+Notes:
+
+- A task begins when all its dependencies (arrows going into it) are fulfilled.
+- The success of setting up rageshake is never asserted, element-web has a fallback path for running without IDB (and thus rageshake).
+- Everything is awaited to be settled before the Modernizr check, to allow it to make use of things like i18n if they are successful.
+
+Underlying dependencies:
+
+```mermaid
+flowchart TD
+    A((rageshake))
+    B{mobile}
+    C((config))
+    D(((olm)))
+    E((i18n))
+    F(((load_modernizr)))
+    G(((modernizr)))
+    H(((skin)))
+    I(((theme)))
+    X[app]
+
+    A --> G
+    A --> B
+    A-- assert -->X
+    F --> G --> X
+    G --> H --> X
+    C --> I --> X
+    C --> E --> X
+    E --> G
+    B --> C-- assert -->X
+    B --> D --> X
+
+    style X stroke:red
+    style G stroke:red
+    style E stroke:lime
+    linkStyle 0,11 stroke:yellow;
+    linkStyle 2,13 stroke:red;
+```