Some improvements in table widget items.

[audetto]

• common function to create all widgets (right justified seems to look better in all cases)
• stick to QVariant where possible to allow sorting (only swim durations are converted to strings otherwise default conversion looses seconds)
• resize columns after editing to fit content
• move more relevant values towards the left
• add number of lengths in set (this is the first thing I look at)
• add lane number