Proper license tags for Crosswalk third-party components

Crosswalk is built on top of Chromium and thus, pulls most of the
Chromium dependencies. This patch clarifies the license of all of
these components, including the ones that are not built/shipped with
the default configuration of this recipe, for the sake of completeness
and transparency.
Add tool for collecting license information of 3rd party components

This tool is a modified version of a Chromium tool for scanning licenses
and generating the web page describing the licenses of the software used
in the browser.

This version can output the bitbake license tags and md5 hashes.
Add layer own LICENSE file