Support for different units for windspeed

Changes:

• added attribute unit_windspeed to change unit for windspeed readings to m/s or km/h
• converted units get rounded to 4 decimal places

fixed bug with disable

Changes:

• Fixed the bug when reenabling the module after disable, it didn't get active again.
• added disabledForIntervals
• attribute WUInterval renamed to interval
• default interval 300 seconds

Bug fix release

fixed some bugs, works now as it should. :-)