[F] fetch file list on dropbox

and some bugs fixed
[F] store plaintext token at cookie

...for the moment. next will build a simple local db.
[F] get blog content from dropbox

add api: files(GET)
split function getBlogContent into 2 func: fromLocal/fromDropbox
no cache for dropbox blog right now
[F] it turns out a wrong way to work with dropbox

remove the dropbox related 'list blog file' func
but retain the others code, they could be used another day
Merge branch 'feature/read-files-from-dropbox'