251 & 212 Migration + new components + callout cards

[jcrayb]

Migrated all 251 pages

Created extra components for extra modularity that follow Latex naming:

• \itemize => =>
  • \enumerate => =>
    1. \item=> =>

  Modified callout cards to add stickyness within section => Cards follow on scroll until end of section. When the screen becomes too small (portrait mode on a phone, < 992px), they now appear at the end of the section

[jcrayb]

NOTE: Changes in this branch depend on some small tweaks from the 251 migration, it'd be a good idea to merge the 251 branch before merging this one.