Don't allow registering certain hokeys

[eug3nix]

There are some keys or key combinations which have some established and well known actions associated with them.
We should not allow the user to override these well known key combinations when binding hotkeys in pgmanage.
Here are some examples (there may be more):

• Ctrl-C
• Ctrl-V
• Ctrl-Z
• Tab
• Shift-Tab
• Arrow keys
• Capslock
• Backspace
• Shift+Arrow keys
• Context Menu key
• Home/End/Pgup/Pgdn