Dashboard timeline: year indicators

[katevda]

When searching for the architect Émile Janlet in the dashboard, this is the timeline I get. It is beautiful, however, not at all clear if he made buildings in a span of 5 or 50 years. Might be a good idea to automatically add the indexes, varying from every 1, 10, 50 to 100 years

[jbelien]

Indeed, timeline should be improved.
Related to #68