Improve SUMMARY Style

[santo-it]

Somehow between 2.0 and 2.1 we lost the numbers of the summary entries - which are useful in my opinion. Not sure if this was intentional

Also, I feel CSS style of the Summary can be improved. Look the style of the summary in @smolinari 's work done in 2015: https://smolinari.gitbooks.io/orientdb-documentation/content/v/7038a670d140a9be5a86364bca2b61bca61f54fc/ : I like the numbers and the color (blue) when the mouse is on a summary link