Improve description of modules

Should we try to make it clear which modules provide actions, and which provide conditions?

Might be an idea to append "Discounts" to the module readable names, eg change "Product" to "Product Discounts"

This is less important now we have moved the all the discount modules into a group on the modules page.

For the description of Product module, change "Discounts on products" to "Discounts on single products"

I have committed this change to both 5.x and 6.x but changed it to "Discounts on individual products."