Build: Move externals from /lib/ to /external/
Build: Add migrateWarn and migrateWarnProp to .jshintrc

Close gh-63
Core, Traversing: Add size & andSelf methods

Fixes gh-60
Closes gh-62
Build: Allow to pass browserSets & jQuery version to testswarm task

So far, Migrate has been tested only on browsers supported by jQuery 2.x.
This commit changes the configuration so that different browserSets can
be tested with jQuery 2.x and 1.x.

Closes gh-59