Create JexlNodeBuilder for creating JexlNodes

[lbschanno]

Create an initial builder library for creating JexlNodes. This library is aimed at reducing the verbosity involved in creating new JexlNode instances, and at reducing bugs introduced by either incorrectly setting or forgetting to set the correct parentage for child nodes.

This pull request also contains a proof-of-concept of the builder library being put to use in JexlNodeFactory for several methods.

[ivakegg]

nice work!

[lbschanno]

@jwomeara I haven't done any extensive performance testing, but you make a good point of its importance, I'll try to get some performance metrics for you.