Adds support for onpaste GoogleChromeLabs#97 (GoogleChromeLabs#98)

* Adds support for onpaste GoogleChromeLabs#97

+ file-drop listens for onpaste, if there is data and it matches the
   type it will use that and raise a custom event
+ Adds a new event on file drop 'onfiledrop'
+ App listens for this event and will map to onFileDrop

* Hoisting getFileData

* The linter seems to think Array.from is of type File, when it's not.

* Remove an entire type of event handler.
+ Removes onfilepaste, joins into 'onfiledrop'
+ Adds 'action' to let you distinguish between the paste or drop
+ Updates app so it just uses the one event.

* Fixing PR issues

+ null return types >>> undefiend.
+ FileDropAction type.
+ remove coercsion on the array types.