Updates to presentation and amount of text in "Categories & Weighting" section of Settings

Currently, there's a pretty massive chunk of blue info text sitting in the "Categories & Weighting" section of Settings:

To make the information here more contextual and easier to digest, can we do the following:

1) Provide the following text immediately below the "Categories & weighting" radio button (if either "Categories only" or "Categories & weighting are selected), above the checkboxes for drop highest / drop lowest / keep highest:

> Note:
> - If 'Categories & weighting' is enabled, uncategorized items will not be counted toward the course grade.
> - A category will only be visible if there is at least one Gradebook item assigned to it.

2) Remove "Enable" from the drop highest / drop lowest / keep highest labels.

3) Provide the following text beneath the drop highest / drop lowest / keep highest checkboxes:

> To apply drop highest, drop lowest, or keep highest to a category, all items in the category must have the same total point value.

4) When either drop highest or drop lowest AND keep highest are enabled, and a value has been entered in one of the columns for a category, we should apply hover text to the corresponding greyed out column for either drop highest, drop lowest, or keep highest that says:

> Drop highest / drop lowest cannot be used in the same category with keep highest.

5) Provide the following hover text for the mutually exclusive "Points" final grade selection and categories & weighting:

> 'Categories & weighting' is not compatible with the 'Points' final course grade display option.

With these updates, the blue info box is no longer needed.