Toshaan Bharvani 602628c969 event updates
* event list is now as discussed
    - call to action buttons
    - no text, just the title
    - date and place
    - cfp is red to highlight
* frontmatter sanatization
* use of shortcodes in place of conditional code

Signed-off-by: Toshaan Bharvani <toshaan@vantosh.com>
..
cta.html Transition homepage and join page, break css into separate scss files
externallink.html add externallink shortcode
pdffile.html add shortcodes for pdffile and slides
prereg.html add an external link to the prereg shortcode
pretalx.html event updates
slides.html add shortcodes for pdffile and slides