Get commands to display from atom.commands global if it exists

This allows this package to use the command registry on revisions of
Atom that include it but still be backward-compatible with the latest
public release which doesn’t have the command registry.
Get specs passing both with and without `atom.commands` global
Merge pull request #15 from atom/ns-command-registry

Make compatible with the new command registry
Prepare 0.25.0 release
Use atom.commands to find commands for assertions
Prepare 0.26.0 release
Dispatch custom events with `bubbles: true`
Don’t trigger minimize event

It’s difficult to prevent this command from actually minimizing the
window on both the released version of Atom and the custom elements
branch at the same time. The easiest approach is just to trigger a
different command.
Prepare 0.27.0 release
Fix typo
Add space before parenthesis
Merge pull request #17 from rhcarvalho/fix-typo

Fix typo
Use the new addModalPanel() method
Add space-pen deps
Use libraries instead of deprecated atom exports