Page-up:down/Home/end key navigation

[Robert Leach]

Similar to how the arrow keys work currently for navigation, but doing intuitively what one would expect when using the keys: page up, page down, home, end. The option key could switch from vertical to horizontal navigation. Also, command used with the arrow keys should mimic the home/end key functionality and shift used with the arrow keys should mimic the paging functionality.

[Christopher Keil]

resolves #40; added same scroll functionality to arrow keys + modifiers (ctrl/cmd, shift); removed KeyListener from GlobalView

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