HTML Widgets; Template Text can now use LESS for better CSS styling

LESS can now be used in place of CSS in HTML Widgets to provide a more stuctured way to define Style Sheets, e.g.:

<style type="text/less">
body {
  border:4px solid red;
  
  > div > div.section {
    border:4px solid green;
  }
}
</style>

The following built-in LESS constants are available:

• @MainColourBackground
• @MainColourForeground
• @ContrastColourBackground
• @ContrastColourForeground