Several changes in one commit (bad me)

 - Speed up main feed list refresh by not downloading feed icons and using
   nested feed list (rather than flat)

 - Update icons on main feed list in background now that they are no
   longer downloaded from sync

 - Cache gson builder as to not take penalty to rebuild it for each parse

 - Perform bulk insert of records into Sqlite DB during main feed list sync

 - Add initial support for shared feed button off story page (still needs a bit of work)

 - Add 'mark item read' and 'mark previous items read' functionality to
   the feed story list view
Merge branch 'master' of https://github.com/samuelclay/NewsBlur