Add "download as" option

[BlobCodes]

Is your feature request related to a problem? Please describe.
In most browsers you can just download an image/video/etc by right-clicking and selecting "download as"/etc, however in wexond you can not do this.

Describe the solution you'd like
When right-clicking something, a matching download dialog appears which downloads the file/page/etc on click.

Describe alternatives you've considered
None.

Additional context
None.