Add new `contemporary` style

[jalopezg-git]

This pull request introduces the new contemporary theme, largely based on classic, yet looking more up-to-date (see below for a screenshot). contemporary features a nice-looking header, incl. a QR-code pointing to \@homepage, vertical timelines that span over a section, and the possibility to add symbols (e.g. using fontawesome5) to the section names.

[!NOTE] This pull request was closed in favor of https://github.com/moderncv/moderncv/pull/173.

Changes

• Add moderncvverticaltimeline.sty, implementing typesetting of a vertical timeline using PGF/TikZ.
• Add a new color theme, cerulean, made specifically for the contemporary style.
• Add style moderncvstylecontemporary.sty, together with new head and body styles.

[jalopezg-git]

Closing in favor of https://github.com/moderncv/moderncv/pull/173.