Bump broccoli-merge-trees

• Bump merge-trees (see #45)

Bump broccoli-less-single

• Bump broccoli-less-single for performance/bug fix (See #43)

Bug fix

• Fix issue where app was undefined and erred (see #42)

Fixes and Nested Addons

• Remove need to override mergeTrees options (#39)
• Add workaround for nested addons (#37)
• Misc cleanup