vimrc: <up> and <down> key now keep cursor line center of screen
vimrc: add scrolloff=1
vimrc: some changes

- use solarized colorscheme
- remove custom fold command
- bind F3 to open nerdtree
- easier command to open file with same directory as current file
gtk: use MediterraneanWhiteNight theme and Faience icon theme
.Xdefaults: a bit more condensed font in terminal