add more support for data: and blob: privilaged urls

Adds logic to override Accept header so certain websites don't serve HTML instead of image. This functionaly copies how the Refer header is overriden and can be disabled if not desired.

Without override the Accept header is:
text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8

With Accept override, the header is set by the menu item that invokes it.
Audio: audio/webm,audio/ogg,audio/wav,audio/*;q=0.9,application/ogg;q=0.7,video/*;q=0.6,*/*;q=0.5
Image: image/avif,image/webp,*/*
Video: video/webm,video/ogg,video/*;q=0.9,application/ogg;q=0.7,audio/*;q=0.6,*/*;q=0.5

These values were copied from what Firefox typical sends as Accept header values in these cases.

fix addon options page not loading properly when viewed in an incognito window

- add "View Audio" button for the audio context menu - thanks https://github.com/Deledrius
- fix issue where new windows were never opened incognito, even if the source was incognito.

Added support for translations of menu items.
Reverted english assigned key back to I

This may require changing userChrome.css, as that was based on the menu text. New CSS provided in description.

- make the menu items be hidden if the page url and the source url match (ie image is already opened)

- make changes to how options are loaded, allowing for default options to fill in missing keys (will be useful if new options are ever added)

fix issue with opening local link in new window

add alternative code path for local file system links with some workarounds

Code clean up for options page - removed duplication of default options
Default option of middle click changed to open in background tab (instead of foreground)

fixed typo and incorrect default options

Added a preference page backed by local storage to control behavior of add-on

Merged in invasive-version of code, this add-on now requires a lot more permissions, but should be more compatible with image sites that block hot-linking. (thanks, https://bugzilla.mozilla.org/show_bug.cgi?id=1699128#c39 )

Added View Video context menu item that functions identically to the View Image menu item, except on videos

Added support for modifier keys when left clicking context menu item:
Shift - open in new window
Ctrl - open in new tab
Ctrl+Shift - open in new background tab
(middle click does not support modifier)

Changed hotkey from I to M to remove conflict with official context open image in new tab menu item.
Removed icon aseprite source file
Minor code clean up