Allowed the Implicit grant flow to reuse access tokens.

It allows the Implicit grant flow to reuse access tokens. This fixes issue #421.
Feedback or improvements are welcome.
However the only flow that does not support token reuse is client credential flow. Should this flow also be supported to reuse its token?
Line is too long. [148/80]<br>Redundant curly braces around a hash parameter.<br>Space inside } missing.