App layout externs (#63)

* Add app-layout externs

Merge pull request #50 from danbeam/patch-3

add more debouncer stuff to externs

Merge pull request #40 from danbeam/patch-1

add ���PolymerDomApi#deepContains

Merge pull request #36 from tommycli/master

Add isLightDescendant extern. Fix a typo.

Merge pull request #34 from tommycli/patch-1

Add extern methods to PolymerDomApi prototype

Merge pull request #32 from PolymerLabs/shadyRoot-shadowRoot

Add externs for this.shadyRoot

Merge pull request #29 from PolymerLabs/customstyle-and-replacechild

Add customstyle and replacechild externs

Merge pull request #25 from PolymerLabs/iron-list-externs

Add externs for iron-list

Merge pull request #23 from PolymerLabs/find-original-target

Document Polymer.Gestures.findOriginalTarget

Merge pull request #21 from jklein24/master

Remove a trailing comma from the templatizer externs because compiler.