Filter swim graphs by stroke type

[alex-hhh]

Currently both session and trend swim plots just take all the lengths into consideration. It would be nice if we could filter them by stroke type, freestyle, breaststroke, etc

Needs to be done in the session plots: scatter, histogram, and quadrant

... and also in the trend plots, where a "Stroke Type" selector should be displayed, when the selected sport is "Lap Swimming"