Updates: Improved Slack integration and more

Some recent updates and fixes:

• Improved Slack integration. Most of these changes are "under the hood" to improve performance. You'll also see that the Preferences dialog now shows existing Slack integrations (if any), an option to disable/delete those, and the ability to create multiple Slack integrations to different Slack channels. 
• Improved error handling for SSO with more detailed error messages; this allows us to more quickly identify and solve problems. 
• Increased the character limit for event titles: The new limit is 1024 characters. 
• Improved the behavior of the event editor with changing window size. The event editor will now re-center automatically if the window size is changed. 
• Updated our import tool to allow importing events via CSV to an existing deactivated sub-calendar; previously, importing events to a deactivated sub-calendar would cause it to be reset to activated. Now the sub-calendar will remain deactivated unless manually activated by the calendar administrator.