Fixed #692: leveraging search:parse to evaluate if's against properties

[grtjn]

Fixes #692.

Adds support to use an if attribute with a boolean expression on any config element, even the root (configuration). It allows expressions like:

• prop EQ val
• prop NE val
• prop LT val
• prop LE val
• prop GT val
• prop GE val
• -(prop EQ val)
• prop1 EQ val1 OR prop1 EQ val2
• prop1 EQ val1 AND prop2 EQ val2
• prop1 EQ val1 AND (prop2 EQ val2 OR prop2 EQ val2)
• prop1 EQ val1 AND -(prop2 EQ val2 OR prop2 EQ val2)

Minus represents NOT. For property names one uses the exact names from ml info, but without ml., nor @ or $. E.g.: if="environment EQ local"

[RobertSzkutak]

From my testing and read of the code I'm very confident the parser and evaluation doesn't execute without detecting an if attribute. Basic test cases I tried all appeared to work. Feel comfortable merging this. AWESOME feature!