FR: provide non-function-key shortcuts for all csysdig operations

Currently several of the function keys have alternate keys which do the same thing, e.g. e instead of F5, q instead of F10. This is awesome, but some are missing alternate keys: F2, F3, F7, and F8. It is beneficial to have alternates for all keys, for at least two reasons:

• Function keys are less convenient to type, because it's usually impossible to find the right key without looking at the keyboard. This is particularly annoying for touch-typists ;-)
• The user might be running csysdig on a terminal which has issues correctly handling function keys.