article: make text field for main body article at least twice bigger

Two reasons for this:

a) current size of text_field to put my main part of article is way too small. It's the same as excerpt and that fine, but if I add bigger image or movie, I lose control of it
b) tinyMCE does not work ok in full screen mode (I already reported this issue), and it seems to be somehow unstable in full mode

I attach a screen so you can see it. It's really small, and makes working harder. Jus make it three times bigger - Newscoop is for writers, they won't mind :)