[REF] Partial backport of c2677880400b988c5dc1b779edb2d7736e81aafe
[FIX] remove application from backport of al's commit previously
[FIX] website: add a bool function field `option_bootstrap_less`

Used in website themes.
This field will try to browse the `option_bootstrap_less` view and
read its active field. It allows to hide/show the `customize_theme`
option in customize without adding a group or a field.