Add view config class in C++

[sc1f]

This PR builds on top of the Table class in C++, defining t_view_config: a unified declaration of what a view configuration object looks like, codified in C++ and then implemented in the binding language.

By storing configuration variables (pivots, aggregates, filters, sorts, etc.) as primitive values, we can implement view_config in binding languages without having to construct abstractions that are only used in the engine (such as t_aggspec and t_fterm). This also encapsulates the primitive-to-abstraction conversion code inside t_view_config, reducing the amount of binding code required to construct a view.

C++ changes

• Adds t_view_config and associated logic
• Use t_view_config for all View objects, instead of t_config
• refactors make_view and make_context into templated functions, as their signatures are now much less complex
• Add [tsl::ordered_map](https://github.com/Tessil/ordered-map) in order to maintain aggregate ordering in the view config
• Remove unused t_config constructors, reorganize the t_config header, remove t_aggspec_recipe

JS changes

• Add view_config definition in perspective.js
• Add utilities to create vectors from Emscripten