Implement saving health measurements

Take climbed meters into account when estimating energy expenditure

Allow 1% rounding error when comparing moving time with elapsed time

Use Celery task queue for background analysis processing

Calculate climbed height meters during analysis

Extract elevation data from FIT and GPX files

Add .gitignore

Increase maximum upload filesize to 50MB

Add missing sample data file for tests

Don't try to parse gzipped FIT files also as GPX

Implement calculation of actual "moving time"

Implement coarse auto-naming for untitled activities

Allow upload of activities without title

Support sub-second timestamp parsing for FIT files

The FIT standard unfortunately does not support sub-second accuracy for
most events.  The (awesome) Android app "GpsLogger II" exports the
fractional part of the seconds (in milliseconds) via the non-standard
field number "252", which we now support when reading FIT files.

Do not try to parse a FIT file also as GPX

Enable builtin Django admin interface

Minor styling tweaks

Implement graphs visualizing HR zones

Move energy expenditure rounding up, to avoid issues with `None`

Only perform HR zone analysis if HR data is available