Processing tag changes

[dmitriim]

Need to listen to following events:

• a tag created (do nothing as we don't know yet if a tag will be used in a course)
• a tag deleted
• a tag renamed
• a tag allocated to a course
• a tag deallocated from the course

On allocated to course event:

• figure out cohort the tag related to by cohort custom field type and id
• create enrolment method for the cohort and a course that tag is linked to

On deallocated to course event:

• figure out cohort the tag related to by cohort custom field type and id
• delted enrolment method for the cohort and a course that tag is unlinked from

On created event:

• create a new cohort and populate custom field type and id
• create a dynamic cohort rule associated with this cohort
• add a tag to a custom profile field
• check if any courses have this tag linked (tags can be created while linking) and create enrolment method for the cohort.

On deleted event:

• figure out cohort the tag related to by cohort custom field type and id
• find and delete all enrolment methods associated with this cohort
• find and delete dynamic cohort rule associated with this cohort
• delete tag from custom profile field
• delete cohort

On renamed event:

• figure out cohort the tag related to by cohort custom field type and id
• Cohort would have tag old name
• Rename tag in custom profile field
• Rename custom field value in all user data
• Rename cohort
• find and rename all enrolment methods associated with this cohort
• rename dynamic cohort rule associated with this cohort