Added scrolling functionality

[morsik]

Scrolling works with n (page up) and m (page down) keys.
Should works with PgUp/PgDn too (as it's coded?), but for some unknown reason for me — it doesn't ;(

[morsik]

Hey, now it's better? ;)

[xrmx]

@morsik thanks for refreshing your changes but it doesn't apply to master, you have to rebase and while at it squash all commits together. You can clean whitespace if you want but do it in a different commit than the one adding the scrolling please.

[xrmx]

@morsik could you please check that my pull19 branch works as expected?
https://github.com/unbit/uwsgitop/tree/pull19

[morsik]

Yeah, looks like works correctly.
Except PgUp/PgDn… I still wonder why, cause I got curses.KEY_PPAGE and curses.KEY_NPAGE straight from curses docs (see https://docs.python.org/2/howto/curses.html)

[xrmx]

@morsik thanks for checking, will remove pgup / pgdown then since they don't work here either.