Tests: Added tests for beforePaste on drop.
Code style.
Added if evt to initPasteDataTransfer. Tests for initPasteDataTransfer.
Added if this.$.types to dataTransfer.cacheData. Tests for dataTransfer.cacheData.
Fire paste events always asynchronously.
Added dataTransfer to the paste command. Tests: dataTransfer in paste.
Tests: check paste event count.
Tests: paste with HTML in clipboardData.
Tests: check paste method.
Tests: separate content and events tests.