Improved keyboard support

[sean-gugler]

Lots of common keyboard shortcuts are already supported, which is great! After using CiderPress II 1.0.2 extensively I find myself wishing for a few more:

• Every menu item should have a keyboard accelerator assigned. (Examples: File/Recent Files, Actions/Edit Attributes)
• In file view, Tab key currently moves between fields. This is redundant with arrow keys; it would be more convenient if (Shift+)Tab changed focus to the (prev/)next UI element.
• Continually hitting Tab key eventually gets "trapped" in the button bar
• F2 to quickly rename a file. Ideally UI would be to edit the name directly in the main view, but for now bringing up the Info dialog with focus on the filename should be enough.
• Press "Enter" to open elected file in Viewer
• In Extract dialog, press "Enter" to invoke the "Select Here" button