adblock support: support for optionally injecting adblock css rules for domain given

[ikreymer]

Supports filtering of Adblock Plus css hiding rules and serving css to hide the specified selectors.

• Can load and parse a text file containing <domain>##<css selector> rules, a subset of adblock plus formatted filters.
• Query param adblockUrl specifies the text file
• Can load a gzipped file.
• The endpoint /mp_/adblock:<domain> will return css rules for that domain, `##
• The endpoint /mp_/adblock: returns all-domain rules, eg. ##<css selector>
• If adblocking enabled, link to css add to the wombat header insert.
• Fixes #166
• Testing: Update examples/live-proxy to support adblock via index-adblock.html
• bump version to 2.18.0

Testing:

• Run yarn run build, then yarn run start-live-proxy. This starts a web server on 10001
• Load a site with ads via live proxy, eg: http://localhost:10001/#https://www.cnn.com/, confirm ads are shown.
• Load a site with ads through adblock endpoint, eg: http://localhost:10001/index-adblock.html#https://www.cnn.com/, confirm adds are not shown.