add a couple of MySQL specific mods to our migrations where we need to use the `TEXT` type instead of `VARCHAR` on mysql.

simplify sample dataset management by adding a column `:is_sample` to the Database model.  also add a new api endpoint which allows us to easily recreate the sample dataset if the user wants to do so.

upgrade the revisions code to work off our new events system so that we can remove some unnecessary code from our api endpoint implementations.

also, included here is a small tweak to the revision model to add a new field/column for :is_creation which is true when we know the revision represents the time when the object was created.

adding in the new view tracking code so that we can have an accurate Recents section on the homepage (implements #938)

finish off card activity handling by adding in ability to track the database & table associated with an activity item.

update the database sync event publication so that we can actually track start & end as separate events but part of the same activity.  to do so we add a :tracking-hash to the events when they are published which is meant to remain consistent throughout the sync, then we implement our activity tracking code so that we can lookup an existing activity item and update it based on the custom hash.

streamlining more of the event bus and activity stuff and rounding things out.  adding new migration which creates the `activity` table.

add new migration which adds :database_id, :table_id, and :query_type as direct columns on the Card entity.

simple migration step to ensure that all current public (read) dashboards are migrated to public (write)

update migration and clojure models, api, and tests to simply add a `display_name` attribute on both Table and Field which should always be available.

add new migration which will drop our requirement to have an Organization for any of our models.  NOTE: we are specifically just allowing the column to be nullable and dropping FK constraints for now.

remove the 0.6.0 migration file because we are now adding those fields as part of the initial tables.