Demo Importer and Import/Export Plugin

Added Import/Export plugin to allow for easy theme and plugin data transfer
Added Demo Importer with 2 pre-made demos "Task Horizon" (Web App) and "Phoenix Falls" (Cafe)
Added option to auto-rotate the Tabs block
Added ability to set a custom rendering tag for all Container blocks
Added presets to Button block
Added better UI for selecting Row block size (Full width / Contained)

Fixed icon select block control to remember which source was last used when re-opening the icon picker
Fixed Image Gallery block → scrollbar option to render correctly
Fixed Block element preview animations to render correctly when using a dark color scheme
Fixed Accordion block to allow clicking on inner links with each section
Fixed Text block animations when loading a page from an already scrolled position
Fixed missing string translations
Fixed Image block effects selector