Feature: UI enhancements

Lots of UI Enhancements:
- File listing now disappears on UI when abort is called
- Moved session ID receiving to when server is messaged to verify space availability
- Fixed scrollbar error where no scrollbar is needed
- Simplified code for verifying capacity and preventing visitor from proceeding if capacity is 0
- Completed feature where user is shown file upload percentage while upload is occuring, a check if successful, and an X if error
- Fixed 'drop files here' height placement
- Fixed potentially fatal error due to user aborting a file upload before the file upload even started
- Feature: Clicking the file to retry after a upload failure is available now
- Updated wix styles so settings can work to customize widget
- Added background color on fully loaded files or ones that have errors while uploading
- Changed wix styles to allow for color change of disabled submit button