Add file type detector for vim statusline.

If the file contains line endings that are either DOS or Mac style, it
will get displayed in the vim statusline at the bottom right, next to
the cursor column number.
Furthermore, .vimrc now contains a list of syntax elements that may be
colour-styled with hi(ghlight), commented out.

... just in case I start to dislike the colours :-)
Display 'tmux' instead of session name in tmux statusbar.

Session name doesn't always consist of the name that was initially
specified upon calling the 'tmx' script.
=> rather display 'tmux' than some numbers