Image API Selector extra fields

[stephenwf]

As per
https://iiif.io/api/annex/openannotation/#iiif-image-api-selector

Following work done in #26 @jbaiter

The following fields are supported:

type		Required. Must be the value “ImageApiSelector”.
region	“full”	The string to put in the region parameter of the URI.
size	“full”	The string to put in the size parameter of the URI.
rotation	“0”	The string to put in the rotation parameter of the URI. Note that this must be a string in order to allow mirroring, for example “!90”.
quality	“default”	The string to put in the quality parameter of the URI.
format	“jpg”	The string to put in the format parameter of the URI. Note that the ‘.’ character is not part of the format, just the URI syntax.

The types only contain region and rotation which are most common for now. The others may be useful additions.