Introduce expression generation system

generator.py generates expressions which are defined in
expressionsToGenerate.txt The generated expressions
are derived from class Expression (see 8167c63a9e4282e88fe0146425542a73ac7a2f66)
and built by using the ExpressionTemplate(CPP|H).tpl

MAnual in src/lib/access/expressions/expressionGeneration/generatedExpressions/README.md