Move mark as read and archive to thread mode

This allows me to do searches to refine the crap in my inbox, and
<shift>-a them right away, instead of `| => is:unread label:<blah> =>
<shift>-T =<shift>N => | -label:<blah> | <shift>-T =a`

All I did was copy over the code to Thread Index Mode and test it. Would
love to write some tests for this if required.

Cheers guys, love sup :-)
migrate psych: deprecate migration script

as old YAML support is getting worse the psych-migration script
for old config files are getting deprecated. for now, while
the migration still works on ruby 1.9 and 2.0 we keep it. but not
necessarily untill these rubies are depreacted.

fixes #266.
travis: enable 2.1.1, dont allow failure
notes: ruby 2 compat
Merge #259: Move mark as read and archive to thread mode
Merge branch 'develop' into maildir-root