[embedding API] Add javadocs for v2

Fixes https://crosswalk-project.org/jira/browse/XWALK-2112
[embedding API] Break links into version 1 and version 2 sections
[run on Tizen] Add note about --fullscreen option for xwalk-launcher
Add page about remote debugging to 'getting started'

Also moved other references to remote debugging to this main page;
then add links to the central debugging pages from the other
tutorials.

Fixes https://crosswalk-project.org/jira/browse/XWALK-483
Merge pull request #136 from crosswalk-project/remote-debugging-483

Add page about remote debugging to 'getting started'
Add 'Crosswalk screens' article
Add details about how to install sample game
Add missing explanatory sections
Minor tweaks after proof reading