Enable re-issue of JWT tokens with refreshTokens

[heysailor]

No description provided.

[heysailor]

Allows improving JWT security as discussed in #52

[heysailor]

Handles the re-issue of expiring JWT tokens - helps fix #52

Adds:

• GET auth/refresh which is called with valid JWT as an Authorization Bearer token, as is usual practice, produces a refreshToken for that user
• POST auth/refresh which is called with a valid refreshToken in the request body, produces a new JWT token for that user
• onRefreshRequest handler which allows block of the refresh request, ie blacklist checking
• refreshTokenExpiry which sets the validity of the refreshToken.

[nickredmark]

Awesome thanks!