emacs: initialise appearance options in one place

near top of file, after package installation, add a block to initialise
some appearance options. some of these options were previously set by
custom, some are new. the options are:

 - hide tool bars, menu bars, and scroll bars
 - inhibit startup screen and have no scratch message
 - show column number in mode line
 - set theme

remove the custom block at the top of the file as it is no longer
necessary.