SiteAPI: rename functions

these are the defaults for API, not per host.
rename them to clearify.
SiteSession: reduce bandwidth usage

if the page has been checked before, skip it.
[1/3] SiteSession: add an option to force fetch
[2/3] PostList: force load under centain condition

1. when we're at the head of the list
2. when we're at the tail of the list
[3/3] PostDetail: force load under centain condition

1. when we're at the head of the list
2. when we're at the tail of the list
[1/3] prepare share function
[2/3] PostDetail: add share function
[3/3] PostList: add share function
clean up and unused debug code.
PostDetail: properly return option state
PostList: properly return option state
PostList: remove unneeded code

don't have to register empty listener when dismiss.