[F] add webhook controller

after finished this feature branch, we'll be able to get notification
from dropbox everytime our files have been changed; and we dont need to
request to dropbox for blog list and blog revision every time. it'll
increase the whole site's speed with decreasing so much web request
[F] add google analytics code on page
[F] add dbCfg file, preparing for including mongodb.
[F] remove a duplicated getToken() call

rename onNotified();
add placeholder for blogList cache mechanism
[R] remove callback in onNotified()

adjust the timing of calling updateBlogListCache()
[R] add version number on all dep in package.json

get ready for a release version(after the webhook feature finished)
[R] seems like i met a require-cycle

time to re-design the architecture
Merge branch 'feature/webhook'