Add field to track Engagement Index for Activities

1. Modify civicrm_activity table to add a new column:

engagement_level INT default NULL Comment = 'Assign a specific level of engagement to this activity. Used for tracking constituents in ladder of engagement.'

2. Upgrade should insert this column in activity table

3. User Interface:

• Include the new field on New / Edit Activity form and View Activity page IF CiviCampaign is enabled.
• Field Label = "Engagement Index"
• Placement = right after the Campaign dropdown

4. Allow import and export of this new field (Import Activities / Export Activities)