Dialogs should use mneumonics (underlined letter key shortcuts) for the footer buttons

It'd be cool to have the first letters of various button labels activate said button label (e.g. [d]iscard, [s]ave, [c]ancel).

For example, if I `ctrl` `w` to close a document, I can then just hit `d` to discard the file. This instead of moving my mouse or `tab` focus to the Discard button and clicking/hitting return.