`guide-key` for all prefixes

guide-key proved useful many times so enable it for all prefix commands
and actually enable the mode.

org-mode's choice of C-c prefix collides with other C-c prefixed
commands, so add an highlight for it.
Enable projectile caching.

I accept the defeat and enable caching because it makes projectile
usable (kinda) for huge repositories.

Maybe I should be using Per-Directory Local Variables and enabling
caching for huge repositories only.
https://github.com/bbatsov/projectile#storing-project-settings
New package: `aurora-config-mode`
New package: `dash-at-point`

Integrates with Dash.app to persue API documentation.
New packages for working with Rust

- rust-mode
- flycheck-rust
- toml-mode (for Cargo.toml)
New package: `rainbow-delimiters'

Enable only for Emacs Lisp files for now.
`smex' command history under '~/.emacs.d/var'
New package: `thrift'

Rather simple package, only syntax hightlighting from Thrift IDL files.
New package: `git-rebase-mode'

I think I've used this once or twice with Magit and it is brought in by
Magit as a depedency but let's keep it.
Remove 'java' from the Org Babel active languages

Very unlikely I'm going to use a non-scripting language in Org Babel.
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