Annotation: Free Text Callout API

[jamie-lemon]

CL ( Free Text Callout ) should be supported.

[ccxvii]

We now support rendering Free Text Callouts in the core library.

TODO:

Core functions to set and get callout properties.

What should these look like? CL is defined by either 2 or 3 vertices (start, optional knee, and end).

How should changing the CL interact with the Rect and RD properties?

Also adds LE (line ending style) property to Free Text annotation type.