Added thumbnails

Added thumbnail by parsing article content

@davidschachter Need offline API support

1. background process should store image for wetportnow cdn urls
2. need offline api to make http requests for westportnow cdn urls
3. Added basic support for uri scheme of the form wnow:// 
4. Detail view handles to wnow:// uri

TODO
1. Offline api to load wnow://uri 
2. Parse detail view and extract relevant content