Move default cipher paramaters to config.h and allow change through

Move default cipher paramaters to config.h and allow change through
configuration script.

Change default LUKS keysize to 256.

Change default PLAIN mode to cbc-essiv:sha256.

Note that you have to specify cipher and mode in plain type,
otherwise there is backward incompatibility.

If you really need the same compatible paramaters, you can compile
cryptsetup using old defaults, e.g:

./configure --with-plain-mode=cbc-plain --with-luks1-keybits=128

git-svn-id: https://cryptsetup.googlecode.com/svn/trunk@151 36d66b0a-2a48-0410-832c-cd162a569da5