Implement #327 Add condition checking the range of a value

Implement #327 	Add condition checking the range of a value

New feature for <condition> elements:
An (optional) element <precision> allows for fuzzy equals checks
example:
<condition>
  <equals>
    <property>/foo</property>
    <value type="double">0.0</value>
    <precision>0.1</precision>
  </equals>
</condition>

This condition evaluates as true if /foo is within [-0.05..0.05]
(both inclusive)
The precision tag works for int, long, float and double propeties.
It has no meaning for bool properties. For string properties,
precision sets the length of the strings to compare.