Rename extensions to add-ons (closes #38)
Initial addon theme implementation
Update dependencies
Avoid locking while updating extensions (closes #35)
Merge remote-tracking branch 'upstream/master'

Conflicts:
	composer.lock
	mysite/code/tasks/UpdateExtensionsTask.php
	themes/addons/templates/Page.ss
Updated to upstream/master.
Removed UpdateExtensionPackages task.

Cleared merge conflict with templates/Page.ss