Context menu, .extent property, mapml-viewer, rollup.js

This release provides a right-click context menu for the map which allows the user to

• navigate history forward/back/reload
• copy coordinates of the right-click location to the clipboard
• provides a default size for the map

This release also renames the autonomous custom element suite to mapml-viewer. mapml-viewer will be the principal tool that this project develops to establish a common baseline of accessibility features for Web maps. As it turns out, creating a customized built-in <map> element fails accessibility criteria, which might (only) be possible to address and correct in a final proposal to extend the <map> element by using native code (i.e. not a polyfill, an actual implementation).

The code provided in this release also has some unit and end-to-end test coverage, as well as being refactored into manageable files for ease of development.