Add missing CommandInstaller require

Closes #3729
Upgrade to language-css@0.18
Upgrade to language-yaml@0.18
Upgrade to language-ruby@0.39
Add tabLength 3

Closes #3724
Upgrade to language-gfm@0.51
Register workspace commands via $::command until compatibility is better

This is a temporary measure.

Currently, commands registered via atom.commands.add don’t mesh properly
with the dispatch of commands registered via jQuery. Didn’t think this
was a big deal until I realized that it broke the ability to preempt
commands on ancestor nodes by calling stopPropagation, which might break
packages.
Move remaining workspace commands back to $::command temporarily
Upgrade to apm 0.101
Prepare 0.137
Attach, show and hide pane item views with native DOM APIs

We continue to invoke SpacePen attach hooks on any shim wrappers
for backward compatibility, but SpacePen wrappers are no longer required
for attoch/hide/show as they were previously. Next: removal.
Use native DOM APIs to remove pane item views
Upgrade to language-todo@0.13
Upgrade to language-css@0.19
:lipstick: Remove unnecessary conditional

`mkdir -p` is an idempotent operation.
Merge pull request #3750 from mlloreda/patch-1

:lipstick: Remove unnecessary conditional
Delegate pane focus methods from workspace to pane container

Fixes #3754
Merge pull request #3721 from atom/ns-pure-custom-element-pane-items

Allow pure custom element pane item views
:lipstick: spec description
Support inline listeners

This extends the command registry to support listeners registered on
individual elements in addition to selectors. The analogy is inline
styles vs selector-based styles. I’m hoping this will be the foundation
of integrating cleanly with legacy commands registered via our
jQuery::command extension.