rearranged sections in vimrc.

plugin settings followed by autocommands seems more logical than the
other way around.

--HG--
extra : amend_source : 8dee9dd7fcf4f9317645362264afdded2aaff976
added plugin vimwiki.

solely for todo-lists and tables.
added vim plugin calendar.

for integration with vimwiki.
removed unused plugin information.

get them back from repository's history if needed.
fixed formatting.