[Log] Provide a default log category for Y.log calls

Set a default log category of info if no category was specified, or the
category specified is not in the list of valid categories.
use visibility:inherit to allow overlays to be hidden
update change log
Fixes #1632
Add YUI coverageOptions for Yeti.

 - Do not instrument files in Yeti.
 - Use ?filter=coverage query to trigger loading instrumented
   files in tests.

Allows for `yeti -c` to use these options without specifying
them on the command line.
[docs] Add mock data to JSONP Gallery example
[docs] Add mock data to JSONP GitHub example
Merge branch 'mock-jsonp-examples' into dev-master
Merge branch 'issue1632' into dev-master
Build files for axis-category-base.
Merge remote-tracking branch 'upstream/dev-master' into dev-master
[docs] Mock data for AutoComplete YQL example
[docs] Mock data for AutoComplete Geocode example
Merge remote-tracking branch 'jafl/calendar-visibility' into dev-master
[calendar] Build

min files are no change.
[calendar] Update the history
Merge remote-tracking branch 'andrewnicols/ylog-missing-categories' into dev-master
[core] Update HISTORY.md
YUI and Loader build for latest Gallery build
[docs] Mock AutoComplete Flickr example