emacs: don't use yas snippets from melpa

use ones in ~/.emacs.d/snippets instead. the default collection has
loads I don't want to use. when I add ones to the new directory I will
keep them under version control.
emacs: remove flycheck from modeline
bashrc: style changes
bashrc: enable C-s as history forward i-search

C-s is bound to forward i-search, but also to flow control stop. and
flow control stop takes precedence by default. rebind flow control stop
to C-x, making C-s work as forward i-search.