Add arrow key shortcuts.

[jinh0]

New Shortcut: Move between bounding boxes by arrow keys

Adds feature requested by @carrieeex in issue #665 to use arrow keys for moving between bounding boxes.

It would be nice if we can use arrow keys (left and right) to switch between different bounding boxes. For example, when users choose "select by BBox", and then click one of the bounding boxes, press the right arrow key would switch to the BBox on the right.

Demo:

Screen.Recording.2022-05-10.at.10.07.06.AM.mov

EDIT:

Arrow keys now move correctly through syllables.

Screen.Recording.2022-05-10.at.11.39.00.AM.mov

[yinanazhou]

Hi, I'm getting some no facsimile interface error message in the console.

For example,

It's the same error message as the one @cadagong is getting. It works well in gh-pages so I think it's related to your changes. Could you two please discuss and fix this?