WiFi power save mode for ICYStream

[sneiss]

If both, WiFi and Bluetooth are enabled, WiFi modem sleep has to be enabled. If not enabled, I get the following runtime error:
esp32 Error! Should enable WiFi modem sleep when both WiFi and Bluetooth are enabled!!!!!!
Activating power save mode when using an URLStream solves the problem.

ICYStream is currently missing a function to enable power save mode. I added a simple function to the ICYStream class:
void setPowerSave(bool ps) { url.setPowerSave(ps); }

[pschatzmann]

The method as been added.