Increase timeout for live docs

Note: it seems that this setting 'idle_timeout' is only used for live
documentation browser pages, so it should be safe to change it without
affecting users' worksheets' behavior.
Make separate config var for pub timeout

Note: the commit message of the parent of this commit is incorrect. The
timeout variable did control all worksheets, hence this commit.
Rearrange config variable descriptions
pub_timeout is useless

Thanks to @ppurka for pointing out that published worksheets are never
interactive anyway.
add options for live documentation timeout to the notebook command
leave doc_timeout to the default value from server_conf.py
increase timeout for live documents to 600s
Merge pull request #1 from ppurka/livedoc_timeout

add options for live documentation timeout to the notebook command
Merge pull request #147 from kini/livedoc_timeout

Increase timeout for live docs