init.el: Change the Melpa URL

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
core/packs/: Enable aggressive-indent-mode

For Clojure & elisp, enable aggressive-indent-mode.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
core/ui.el: Enable transient-mark-mode

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>