Add Tools page, remove duplicate tool doc, add "What not to commit" page

Staged at:

http://tools.dart-lang.appspot.com/tools/
http://tools.dart-lang.appspot.com/docs/editor/
http://tools.dart-lang.appspot.com/docs/sdk/
http://tools.dart-lang.appspot.com/dartium/
http://tools.dart-lang.appspot.com/tools/private-files.html
http://tools.dart-lang.appspot.com/eclipse/

Review URL: https://chromiumcodereview.appspot.com/13099002