Compress GXP files

[bpatrik]

I checked my GPX files that I logged with my Garmin watch and it seems to contain too much information. GPS entry logs are every 2 meter, every 2-3 sec. It also contains altitude and hearth rate. The app can only use the lat and lon part of the data, so no need to send all of them to the client side. Also data can be more sparse.

Lest implement a lossy gpx compressor: It would remove all not used data and make the entry more sparse.

[bpatrik]

Made some tweaks and tested on my walks, hikes that I recorded with my watch. With this lossy compression a 6x improvement can be achieved.

[bpatrik]

Running the compression on my full gallery (265 gpx files)
Downloaded file size got reduced from 67.8 to 30.8MB