CB-2606 Documented icon usage

1. iOS, Andoroid, FirefoxOS, Windows8, WP8
2. Related PR with support https://github.com/apache/cordova-cli/pull/126
CB-2606 Moved back BB10, Tizen; sort alpabetically
CB-6526 Clean up formatting and minor content
CB-6530: Update plugin documentation locations after removing dev branch
CB-6530: Update plugin documentation locations after removing dev branch
CB-6491 add CONTRIBUTING.md
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/cordova-docs