Add keyboard 'Accelerator' support for Menus and Button

[Orbisman]

Keyboard 'Accelerator' is when you have a character defined so if the user presses the <alt+f> keys for instance, if a main menu of [ File ] is present with the accelerator added, the File menu will be presented. This behavior would work the same for the button.

The Accelerator will be defined as a KeyStroke() class.

Benefits: In said of traversing thru the components, this would be a short cut for the user.

[Orbisman]

For context, From the Microsoft Windows User Interface Guidelines (1992, Microsoft Press),

Accelerators

Accelerators are key combinations that help the user to select a menu, or a command within a menu, without using the mouse.

For example, pressing ALT+F opens the File menu, and pressing ALT+F followed by S chooses the Save command.

Because accelerators follow the same hierarchy as menus, users can learn them easily. Use them to make the program efficient for experienced users, but make sure every command that has an accelerator is also available by using the mouse.

You can show the key letter of an accelerator by underlining it in the menu name or command. Users can then see which keys to press.

Shortcuts

Shortcuts are key combinations that activate a command directly, without first opening a menu.

For example, pressing CTRL+S immediately saves the current document, while CTRL+O opens a file.

A question for @mabe02, I see the InputFilter class, is the intent for this to be like "Shortcuts" or global hotkey ? Not seeing any examples on usage. My thought is to have ability to define "Shortcuts" on the global level, multiple ones, wasn't thinking about the component level. Like the old Norton Commander/Midnight Commander and the Functions keys. Don't want to redesign or add addition code if not necessary.

I currently have the Menu/button accelerators working on my production code, wanted to tweak to be more inline with other GUI standards (Microsoft guide) before providing the pull request with global shortcuts support.