Resolve "Consolidate angles, arrows, and chevrons"

Closes #88 (closed)

Our SVG library has different labeling and categorization for similar icon concepts. This is an effort to begin the process of simplifying the categories and establishing definitions. We primarily use chevrons, and that will be the main category moving forward.

Process

1. Duplicate some icons to establish new naming conventions. This means that angle-double-left and chevron-double-lg-left are the same icon, and exist together for a time, so that we can incrementally change instance names in the product.
2. Rename icon symbols in Sketch to prevent any new designs from using old conventions
3. Once icons with new names are available to the product, begin updating instances
4. After all icon instances in the product have been updated, deprecate duplicate icons that use the current naming convention in the SVG library