Release v0.30.0

• 🌟 New feature: Layouts - new "Sections" level: each layout can now hold several sections (the left-hand menu), each with its own tabs; export/import works per section, and a per-layout default section is used on open and for idle-return
• 🌟 New feature: Design - settings now cascade global → layout → section: theme, typography, grid, guidelines and tab bar can be overridden per section, and header, layout menu and idle-return per layout
• 🌟 New feature: Design - optional toggles to show the section menu and the tab bar even with a single entry (previously only shown from two)
• 🌟 New feature: Tab bar - can now be positioned at the bottom (footer) instead of the top
• 🌟 New feature: Layout menu - datapoint elements: pick the datapoint via the standard picker, and the template field supports HTML