#495 Reviewed the logs design

* Changed the colors if icon and border for sentences
added/modified/deleted, making them less pale.
* Added background color on sentence text, this allows to reduce the
font-size since the text is better highlighted.
* Aligned username on the right side.
* Clicking the date leads to the sentence page.
* When hovering the contribution, the sentence id and the date change
color to give a hint that they can be clicked to go to the sentence's
page.