Disable 'copyindent'

This seems to be responsible for adding some tab literals in a few weird
corner cases:

- Python, when adding a new line following an open parenthesis or
  bracket.

- Commit messages, when creating a bulleted list where I expect to have
  a hanging indent.

I am reasonably sure that I ended up copy-pasting this line, and didn't
actually understand it at the time, so I am removing this.
Remove commented out lines

Now that I am tracking this file in git, it feels silly to have these
commented out lines. If I want them back, they will exist in the git
history.
Consolidate invisible character options in vimrc
Show hard tabs in html files

I'm no longer working with html files that have hard tabs encoded. I'll
override this as necessary if those projects come back.
Improve spellcheck comment in vimrc

I just did a double-take trying to read this comment. Oops. Let's make
that a little easier to read.
Add vim Python ftplugin

From Python PEP-8:

    Use 4 spaces per indentation level.

Since I am explicitly setting my global tabstops to '2', I need to
override this specifically when working on Python projects.