[vim] Allow `backspace` in insert mode

By default, on some systems, `backspace` won't delete over line breaks,
or automatically inserted indentation, or the place where insert mode
started.

This commit changes the behavior mentioned above by setting
`backspace=indent,eol,start`, which basically informs `vim` to allow
`backspace` over everything else.

Ref: http://vim.wikia.com/wiki/Backspace_and_delete_problems
[init] Add `cfprefsd` to the `kill process` list

Starting with Mac OS X Mavericks preferences are cached, so in order
for things to get properly set using PlistBuddy, the `cfprefsd` process
needs to be killed.

Thanks @chdiza.

Ref: mathiasbynens/dotfiles#330.
[init] Clean up `osx.sh`

* Remove/Update settings that no longer work in Mac OS X Mavericks.
* Remove settings that were barely used in the past.