Switch from node-sass to dart-sass

Fix data labels on horizontal bar charts

Issues #546: Reformat multihighlight plugin

Update flot and marked

Issues #546: Update flot to 3.2.2

Remove older tmp SCSS files

Update themes in Sass

Rename tessera files to distinguish themes vs. core

WIP: Darkstrap

#551: Completely revamp CSS theme generation

#551: Build Bootstrap (default theme) from SCSS

Issue #557: Remove toggle interactive button

Update bootbox

Patch for favorites error - the favorites code needs reworking

Update axios for CVE-2019-10742