Improve "Hello World" sample

* Don't require the developer to modify the redirect_uri field of
  his app.  Instead, we put the redirect_uri right into the
  sample app itself, as a command line parameter.
* To avoid confusion, only have the string "YOUR API KEY HERE"
  appear in the source code in places where the developer actually
  needs to change it.
Fix RevokeOAuthRequest to use correct URL

https://www.box.com/api/oauth2/revoke
not
https://www.box.com/api/2.0/oauth2/revoke
Merge pull request #26 from mmorearty/improve-hello-world

Improve "Hello World" sample
Merge pull request #27 from mmorearty/revoke

Fix RevokeOAuthRequest to use correct URL
set charset in constructor of MultipartEntityWithProgressListener
Merge pull request #28 from box/utf8

set charset in constructor of MultipartEntityWithProgressListener
fix a typo that made content_created_time wrong for a new uploaded file
Merge pull request #31 from box/createdate

fix a typo that made content_created_time wrong for a new uploaded file