Add possibility of peeking primary screen

Good explanation from Tomaz (he's better with words than me):
    I think he wants to quick swap the text from primary and secondary screens:
        ls folder
        vim somefile.txt
        - mmm, what's the name of the file I need, I just did the LS for that reason -
        peek into primary screen, note the file name, go back to secondary screen

Merge request:
!210