Add support for resizeable terminals

[ismacasti]

This is a small change to the ui code, that makes it adapt to resized terminals. It just listens to the ncurses signal to update the h, w and hw variables. It also paints the header every time.

Works quite well.

[vedranmiletic]

Tested on Fedora 24 with a Fiji card. Works well.

[clbr]

I tested in xterm, rxvt and mrxvt. In the first two it passes, but in mrxvt the VRAM bar gets drawn wrong, one char left to where it should be.

Pic:

Now, this may be a mrxvt bug, but I'd appreciate if you looked into this.

[ismacasti]

It seems mrxvt prints the cursor when resizing, ignoring ncurses' curs_set(0). It's probably a bug on mrxvt, but anyway, now I set the cursor at 0,0 before refreshing. That will just put a black character square at the beginning of the header.

[clbr]

Thanks!