Support for String and Number items in pilight binding

This update for the pilight bindings adds support for getting string and number values from pilight, for example temperature readings from a 433Mhz weather station.

[Updated wiki page](https://github.com/idserda/openhab/wiki/pilight-Binding)
We are trying to avoid caching Items wherever possible. Since you are just going to use the name and the class for later conversion do provide these two single parameters instead of caching the Item