Avoiding closure leaks

[andrija-hers]

The proposed PR gets rid of memory leaks that are introduced via "closure leaks".
The main problem was within the validateSchema method of the Validator class.
Three closures were produced there: shouldResolve, resolve, and an <anonymous> one.
These three were mutually dependent. However, shouldResolve depends on no outer params, so it was taken out of the validateSchema and promoted to a standalone function.
resolve became the superResolve method, and the <anonymous> one became the schemaTraverser method of the Validator class.

In the same manner, the code in helpers.js was cleared. Affected are:

• deepMerge
• importErrors method of the ValidatorResult class
• toString method of the ValidatorResult class
• encodePath method of the ValidatorResult class

[tdegrunt]

Thank you!