Vim: improve update script

My update script wasn't quite doing what I wanted, because of the order
of the commands it was executing, so I reconfigured it a bit.

This was mostly borrowed from @wincent's update script [1]. 3 key
differences:

  1. I made it run YouCompleteMe's install script every time it is run.
     It only takes a minute or two to install, and I don't run the
     update script very often, so I don't mind paying this penalty every
     time since it is likely what I want to happen anyway.
  2. I made it install Command-T every time. Similar to YouCompleteMe
     above.
  3. I left out the rev-pinning. I like to live on the edge, which means
     that I am always using latest master for my Vim plugins. I decided
     that I'll roll without this feature until I actually have a need
     for it.

[1]: https://github.com/wincent/wincent/blob/master/update-bundle.sh
Vim: update bundle
Vim: remove unnecessary placeholders from snippets

The vim-snippets README has some guidelines for writing snippets. One of
these is "Don't add useless placeholder default texts". I'm taking that
advice to heart and removing my useless placeholder default texts.

While I was at it, I also fixed a soft tab in one of my snippets.

https://github.com/honza/vim-snippets#policies--for-contributors
Vim: improve JavaScript snippets

I decided to git rid of vim-snippets because it contains too many things
that I never use. Instead, I want to have a solid set of snippets that I
actively use and that are tailored to my coding style. I am starting
with my JavaScript snippets, fleshing out a few things that I used from
vim-snippets.
Vim: remove reselect visual block after indent/dedent

I tried this out for a while and in the end decided that it slowed me
down more than it sped me up. Removing it to get faster again.
Vim: add mappings for Tabularize

I frequently want to use Tabularize to align things on `=` and `:`, but
typing these things out every time is tedious. A couple of visual mode
mappings should do the trick.