KNXCoreTypeMapper maps Openhab's PercentType to KNX's DPT_PERCENT_U8 and
vice versa. PercentType holds values from 0% to 100%, but DPT_PERCENT_U8
can hold values from 0% to 255%, where byte 0xff is 255%. 
A better match is DPT_SCALING (5.001) which translates byte 0xff to
100%.
So, 5.001 and 5.004 should now behave as spec'd in KNX Spec.
Replaced static KNX id Strings with calimero id lookup methods
Merged workaround regarding Float to String conversion on calimero
Merge branch 'KNX_percentage' of https://github.com/snow1111/openhab into snow1111-KNX_percentage
Merge branch 'snow1111-KNX_percentage'