Improve UI

[NicoPennec]

Problem

• Some outdated npm dependencies.
• Style issues with tables from markdown (related to Dark theme: Markdown table row unreadable on hover, headers hard to read #1471).
• On notifications, a translation is missing.

Solution

• Bump npm dependencies: Marked v4 to v13
• Fix rendering of tables from markdown, especially in dark mode.
• Add a missing i18n key on the Notifications page.