Add types to columns

[joffrey-bion]

A few types that would be very useful for extra processing:

• free text (of course, by default)
• date / timestamp (to format differently, or use a threshold)
• numbers, IDs (to filter with thresholds)
• jsessionID (to filter by session, and maybe create tabs based on that)
• class name (to display simple class names, or even create links)
• severity (to know the finite set of values, to be able to order them, and filter)

Compared to free text columns, that would open a LOT of possibilities...