Add page up/page down support in process logs.

[tleavitt]

I've found myself spending a lot of time holding the up and down arrow keys to examine the process logs. It would be nice to have page up and page down functionality to make this faster.

Unix standard is to map 'd' to page down and 'u' to page up. 'd' is currently reserved for the debugger, so we could map 'shift + d' and 'shift + u', say.

While we're at it, a shortcut to jump to the end of the log would also be nice. In vim and git this is 'shift + g'.

[tleavitt]

Addressed by #78