Problem: if you use uBlock Origin, and enable the
"Fanboy's Social" filter list, Healthchecks does not show
Telegram or WhatsApp icons. This is because the filter list
contains "##.icon-telegram" and "##.icon-whatsapp" entries.

This commit changes the CSS class prefix to "ic-". So we're
now using icon classes like "ic-telegram" and "ic-whatsapp".

As a bonus, we save 2 bytes in HTML per displayed icon :-)

Fixes: #202

Fixes: #428

Not using them anywhere on the site currently, so commented them out
in bootstrap.less and regenerated bootstrap.css.

Fixes: #462

Fixes: #450

Fixes #282

Fixes: #436