workaround for registering currencies (getLatestCDD fails on server implementations)
added mintkeys property
added client property (caches htppClient per currency)

Signed-off-by: Gulliver <gulliver@fargonauten.de>
added "Advanced Section" showing the mintkeys
implementation uses now [OCCurrencies currencies]
implementation changed to use [OCCurrencies currencies]
tests refactored to support test on both server implementations