Minor changes:
- standardise cell background colours on both transaction search and other transaction lists
- re-word "inbound email" and "outbound email" to "email received" and "email sent"
- hide technical details of email bounces behind a details disclosure
- improved pagination of the printable event attendee sheet
- remove old doc_type attribute in objects' D
- improvements to WYSIWYG editor
- convert height and width in style attribute on images into height and width attributes (fixes for Outlook)
- new content_object and selector_object picker (gradually being rolled out on all relevant forms)
- upgrade paypalrestsdk to fix several bugs in PayPal's SDK (also involved updates to around a dozen other modules)