push-guestbook: Added retry logic to the client.

Formerly, if there was an error in the client's connection
to the server, it would just quietly bomb out and fail to continue
initializing its state.  Now it will retry every 5 seconds.  Note
that if getChannelId fails it will still just not function correctly.
added screenshot thumbnails and a new generic README.md
Merge branch 'master' of github.com:GoogleChrome/chrome-app-samples
added small version of CWS tryitnow button
fixed wrong sized try it now image
bumped versions to force republish
fixed CWS id of keyboard-handler and window-state samples
Merge pull request #128 from mrdewitt/push-guestbook-retry

push-guestbook: Added retry logic to the client.
Use notifications instead of polling in the Windows sample app
added screenshot for gdrive sample
Merge branch 'master' of github.com:GoogleChrome/chrome-app-samples
bumped version to publish
removed unused domain permissions;
fixed API key
replaced chunck upload by the upload.js from drive team; removed gdata header
fixed progress bar of gdrive
bump version
added gdrive screenshot to readme
Fix SystemInfo API docs.

Correct document links in README.md.
Merge pull request #140 from hokein/fix_system_info_api_doc

Fix SystemInfo API docs.
url_handlers sample (Mobile Wikipedia Viewer)