Determine the preferred human readable title of a topic

[cirosantilli]

Topic are grouped by ID. But when displaying:

• the header of a topic page
• a list of topics e.g. at: List topics on home page #255

we will want to somehow determine the human readable title of the topic, which might vary across authors, e.g.:

• JavaScript
• Javascript

both have the same ID javascript and are therefore grouped.

We will likely use some simple algorithm like "look at the top 10 most voted articles and pick the most common one".

This is likely only feasible if we add a Topic table.

[cirosantilli]

Fixed at: 70b8675