change spec labels

[dret]

currently, a "Web API" label shows up on specs that define javascript APIs. most people would probably classify those specs to belong to the general "HTML5" ecosystem of specs: http://html5-overview.net/
for most people, a "Web API" is one that is available via HTTP, and none of the specs labeled "Web API" on the @w3c site are about this kind of API.
on the other hand, WebSub actually is a "Web API", but is not labeled as such.
i would recommend to:

• rename the "Web API" tag to "HTML5" to match the most commonly used terminology.
• use a "Web API" tag for specs such as WebSub when a spec actually is about an HTTP-based API.