[package] Use elpa repository

Needed for auctex
[base] change require handling in cb:declare-package-installer

Do not throw errors by attempting to require packages that do not
declare an eponymous feature, e.g. auctex.
[tex] Use standard faces for latex errors
fixup! [base] change require handling in cb:declare-package-installer
[latex] use flycheck face for latex errors
[idris] add "default total" to file template