Source everything from (M)ELPA. Separate packages

Following the 'lisp' directory, also drop 'themes', installing "Tomorrow" theme
from MELPA.

Move all third party package descriptions done via `use-package' to a separate
file `packages.el' and also assign it a register to easier jumping to it when
necessary.
Simplify the way we enable some disabled commands

Drop the unnecessary `defun' and just `dolist' the list of disabled commands we
want back.
Hook `hl-line-mode' to `prog-mode-hook'

Highlighting the current row is useful for almost all programming language major
modes.  Some major modes still doesn't invoke `prog-mode-hook' but it's rather
new so eventually they'll start invoking this hook.  For now we'll add them to
`hook-into-modes' expressions, next to prog-mode-hook.
goto-line-with-feedback: Full URL to origin

Replace the misspelled domain to the origin with a full URL to source specific
post for easier reference in the future.
`org-replace-disputed-keys'

Stop 'org' hijacking shift-arrow keys, replacing them with more Emacs idiomatic
meta key based shortcuts.