Add Setting for Course Section Background Colour

[Jeremy Hopkins]

We seem to be missing a setting for the course section backgrond colour. This should be added under the "course formats" settings page.

[Manoj Solanki]

Fix #725. Note there is no background color for each activity yet. This requires a style declaration for every mod type available in css. To discuss.

→ <<cset 80dac5708e51>>

[Manoj Solanki]

Added background colour settings for specific activities. Part of fix #725.

→ <<cset b5ecdab598ee>>

[Manoj Solanki]

Please test.

[Manoj Solanki]

During further testing I think I've found an issue with displaying the course page. Will update soon.