CORE-4160 Added ToolRequestHistoryDialog.

Added a ToolRequestHistoryDialog for displaying Tool Request Status history, opened from the Notifications grid.
Refactored the Notification payload field into a Splittable.
Added Notification Payload AutoBeans for Data and Tool Request notifications, and refactored NotificationPayload into PayloadAnalysis for Analysis notifications.
Added ToolRequestStatus enums.
Added an IplantContextualHelpStrings accessor to the I18N class.
Removed obsolete NotificationAnalysisContext AutoBean.
Minor refactor in NotificationMessageCell.