Drag and drop style works!

Gonna pull in upstream develop.
merged with develop. Started moving javascript to SynJSNIUtils. Cleaning
up drag&drop zone.
moved event handling for drag and drop to SynapseJSNIUtils.
Made some constants and did some clean up.
centered the 'choose files' button in the drop box.
Used negative margins for Drag & Drop message.
Got rid of some unneeded constants.
merged with upstream develop
Finally got the 'Drag & Drop' label to not block drag and drop behaviorclear
Merge branch 'develop' of https://github.com/Sage-Bionetworks/SynapseWebClient into SWC-1382
made sure the event handling would only be added to the browser once.
Modified addDropZoneStyleEventHandling to have the private method access the static variable so that the field name could be changed.
Moved the event handling to the view rather than the uploader.
Got rid of dropStyleName parameter in public non-native addDropZoneStyleEventHandling, as it was not configurable. Now just access UploaderViewImpl.FILE_FIELD_DROP_STYLE_NAME when handlers are added to document.
Merge pull request #1181 from toddis/SWC-1382

SWC-1382