Disabling Javascript breaks some browser functionality

Nobody has claimed this yet.

**Current Behavior:**
Disabling Javascript breaks the Luakit settings page and some other functionality (e.g. bookmarks adding).

**Desired Behavior:**
Disabling Javascript should not affect browser UI functionality itself.

**How can we reproduce it (step by step):**
1. Disable Javascript (`:settings`, uncheck `webview.enable_javascript` checkbox).
2. Restart Luakit browser.
3. Go to some web page and try to add a bookmark (`B`).
Bookmarks page with filled popup dialog appears, but on Save, empty page appears (possibly with already existing bookmarks gone), and the bookmark is not saved.
(Neither `:bookmark URL` works, as it triggers the same UI.)
4. Try to enable Javascript again (the checkbox label does not change to green "Enabled", which might not be noticed at this time). After browser restart, Javascript is still disabled. User realizes that the settings UI is practically defunct.
(`:set webview.enable_javascript true` +restart works.)

**Environment:**

Linux Distribution & Version: Arch linux
```
luakit 2.4.0
built with: webkit 2.46.6 (installed version: 2.48.3)
GTK 3.24.49
GLIB 2.84.0
SOUP 3.6.4
```

Reproduce the issue through :settings by disabling webview.enable_javascript, restarting, then trying B and :bookmark on a web page. Trace the settings checkbox and bookmark popup flows, including Save, and verify that browser UI actions still work and the setting can be re-enabled after the fix.

Written by the indexing model from the issue text.