add isEqual() function into condition Operand class

[andrewtelnov]

We need the way to compare two expressions.
These two expressions are equal: "{queston1} == 1" and "{queston1}=1", but we can't compare them as strings.
It could be checked as:

const op1 = new ConditionsParser().parseExpression("{queston1} ==   1");
const op2 = new ConditionsParser().parseExpression("{queston1} =1");
console.log(op1.isEqual(op2)); //it returns true