Add samples to projects window #187

The most important part of the app is to teach people. We can provide our samples for learning purpose.

It can be achieved by on-demand resources.

Tasks

• Load single document
• Create sample json and put it to samples folder at Samples repository
• Add cache
• Output samples document by loading preview only
• Add tab for samples
• Calc available languages on the fly
• Apply language selection
• Select language according to current locale
• Divide sections by projects
• Reset language submenu after loading
• Save document when close the one
• Save document to language folder
• Strange behaviour after saving
• Show samples if there in no user's documents
• Remember selected language
• Remember last opened tab
• Remove samples that is not presented in structure.json?

Image loading

• Add icon to show that loading is needed
• Prefetch and cache samples structure
• Add loading state for previews and for document
• Update images after loading
• Save preview to .heic
• Support old-versioned .png preview
• Check why cloud document's won't read preview
• Image disappears when black-white appearance changes
• Update samples to new structure
• Load documents' previews in parallel
• Draw elements over preview's image #224

UI tests

• Structure loading
• Language can be changed, but remember last selection between tab's switches and restarting

Preview

• Add samples to preview #225

Infrastructure

• Add file version property to make graceful updates
• Add file size to track downloading progress
• Create a tool that create json with samples structures
• Add this tool to GitHub CI
• Add more samples for Pizza, remove samples for Drinkit (we should make more samples for different languages)
• Reload document if version changed. Add version to regular document?