Use zsh's default for ':completion:*:hosts'

The manual configuration of ':completion:*:hosts' causes some problems
(e.g. issue #1337), and misses useful information (especially from
~/.ssh/known_hosts; issue #690 and issue #1009).

The best option appears to be using zsh's default configuration for
':completion:*:hosts'.

While rebasing this for a new pull request (#1498 got closed by accident
and then requests to re-open it got ignored), it also drops the `users
off` setting: completion of user names can be useful, and the commit
adding it (c4434d2) does not state why.
Merge pull request #2602 from blueyed/use-default-hosts-completion-2

Use zsh's default for ':completion:*:hosts'
Add 'chris' theme
Update zsh prompt
Add custom dir to repo
Remove Climate aliases
Remove spec alias
Add irc alias for weechat-curses
Remove before and after context on grep alias
Add gap alias, remove grep alias
Add custom scripts to repository
Rename scripts to have correct load order
Remove unnecessary init scripts
Change LSCOLORS to better match Thayer color scheme
Move path stuff to oh-my-zsh config
Add node binaries to path
Remove custom LS colors for zsh
Remove custom Square stuff
Remove DYLD_LIBRARY_PATH from environment
Add alias for sending tmux buffer to pbcopy