Users can now mark individual cards with one of four different coloured
flags, instead of relying on a tag that applied to the whole note.
- replaced marking functionality in reviewer and browser with new
flag options
- added flag:x search
- marked and leech tags now show in normal tag list in filter screen,
instead of being treated specially
- the other clients will need updating to set and shown the flags, but
flags set in the beta should be preserved by the other clients
- the bulk of image use is in webviews, so we move almost all used
images to web/imgs, as it's easier to manage
- change AnkiWebView to always use the local media server as a base, as
much of the UI has come to depend on it
- remove images from a few areas, as they felt dated
- delete a bunch of unused images
- href=# links were being opened in a browser window, so the code now
ignores them - the HTML should really be updated to return false in the
onclick handler
- update a few icons
