Import Heart Rate data from swim activities

[alex-hhh]

Garmin HRM-Tri and HRM-Swim Heart Rate monitors can record HR data for swimming activities. These devices store the data on the monitor itself while submerged and it is sent to the main device at the end of the activity. The resulting FIT files record the HR data as additional FIT files appended to the main one. These are called chained FIT files in the documentation.

The main issue is that normal FIT lap swim activities only record pool lengths and no data during the crossing of that pool length. We only store one pseudo track point for each lentgth which is needed as only track points can record distance. The lap swim data is in the length entry and data frames for swim activities hold lenghts and not track points.

This will have to play nice w/ the swim lap editor. In HR data will be time based and we will have to correlate it somehow with the rest of the activity which is lap/length based.

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Update (27 Aug 2021) Pull request #75 added support HR data in lap swim activities, the following are remaining tasks:

• [ ] import HR data from lap swim activities where a HR chest strap is used -- these FIT files are using "chunks", that is multiple FIT files concatenated together
• [ ] update scatter the session inspector to allow selecting HR related data series in scatter plots and best-avg plots
• [ ] update the trend charts to allow selecting HR related data series for trend charts when lap-swimming activities are selected (histogram, scatter, best-avg)
• [ ] update the sport zone editor to allow adding HR zones for lap swimming and update the model parameters page to show the zones.
• [x] fix the lap swim editor to handle HR data (currently HR data is lost when lengths are split or merged), see #79

[alex-hhh]

Also check f0030.fit (and associated notes), which has inline HR data, which is imported correctly, but not shown in "Lap Swimming" mode (only in plan "Swimming" mode).