Add Activity (Course Module) metadata to support learning analytics

It would be helpful to include a float "expected time to complete" value (in hours) with each activity for learning analytics purposes.This could be used in a number of types of models:

1. If students are spending much less than the expected amount of time on an activity, as the activity expect completed by date approaches, the system could remind the student to engage in the activity
2. If students are spending much more time than expected on an activity, the system could notify the instructor that the student appears to be struggling with the activity
3. During the instructional design phase, if the total estimated time for activities does not match the time estimate for the course (see MDL-59022), the system could notify the instructor or another role (e.g. a course developer or instructional designer role) that the course may need review. This could be relevant whether the total expected time of activities in the course is much lower or much higher than the total expected time for the course.

For instructor convenience, it should probably be possible to adjust these values via one spreadsheet-like overview page for all modules in the course.

An option should be provided per activity to show or not show the expected time to complete the activity on the course page, similar to the current option to show the activity description.