[Fix #552] Load resources from jar/zip files efficiently.

Instead of loading the entire `.jar` file into a buffer, just
extract the single resource to be displayed. Mark it read-only.
If that resource is already open, reuse it.
[Fix #589] Don't prefer local paths over tramp by default.

Rename `cider-use-local-resources` to `cider-prefer-local-resources` and
set default value to nil.

Remove `cider-home-prefix-adjustment`. It was unnecessary, and a bug in
`cider-emacs-or-clojure-side-adjustment` prevented it working
as (apparently) designed anyway.

Rename `cider-emacs-or-clojure-side-adjustment` to `cider-file-path` for
clarity (and brevity!).
Merge pull request #599 from jeffvalk/master

[Fix #552] Load resources from jar/zip files efficiently.