* Revert escape-string-regexp  back to 1.0.5

This broke IE 11. See issue https://github.com/sindresorhus/escape-string-regexp/issues/18Signed-off-by: Kyle Keating <kkeating@hypothes.is>

* Fix es2018 polyfill so it does not break IE11

Promise is undefined in IE11.
Signed-off-by: Kyle Keating <kkeating@hypothes.is>

* Add user-agent shared util

Adds 2 helper methods:
- isIE11
- isMacOS
Signed-off-by: Kyle Keating <kkeating@hypothes.is>

* Fix IE11 keyboard events

- IE11 uses special names for arrow keys that are different than the standard key names.
- Fix handleOnInput in tag-editor for IE11
- use isMacOS in markdown-editor

* Add renderer-options.js module

This module holds any renderer options to globally fix browser quirks or any other unique customizations we wish to add.

The dir=“auto” causes an exception in IE11. ie11DomReassignments() will simply replace that attribute’s value with an empty value so it does not break.

* Add browser-compatiblity-utils module

Current only holds one method used to translate key names used by IE11 to standardized names that all components can assume. This removes the need for special cases in each component when listening to keyboard events.

* missing code cov