Support for Edge Browser

[rthaut]

Microsoft's Edge browser supports Extensions, so it should be possible to bring DeviantArt Filter to Edge now.

The build process for version 5 currently generates an Edge version, but the generated extenion does not actually work, primarily due to the Microsoft Edge extension APIs using callbacks, not promises.

Support for Edge may need to wait until either Mozilla's Web Extension polyfill supports Edge (see this issue), or until the Edge team switches (or at least supports) promises. Alternatively, if there is a better/different polyfill that adequately closes the gaps between Chrome, Edge, and Firefox, we should explore switching to that polyfill.

[rthaut]

DeviantArt Filter is now available on the Microsoft Edge Add-ons site.