new very large sample files

[Dirk Hohndel]

For those who like to test with very large sample data, I have created
(with the help of one of our members here - thanks for that) an anonymized
dive log of substantial size. 8064 dives, 4.19M samples.

You can find it here:

https://github.com/Subsurface-divelog/large-anonymous-sample-data

GitHub wouldn't let me upload a 200+MB file, so you need to clone the repo
and then uncompress the file.

And you can also access the same dive data via git storage (intentionally
not from our cloud server, but from GitHub as well - actually in the same
repo):

./subsurface https://github.com/Subsurface-divelog/large-anonymous-sample-data[git]

This hopefully will help with reproducing some performance issues and
maybe even some of the crashes people have reported.

Admittedly, for me on ArchLinux this file does not allow me to reproduce
those crashes in 
https://github.com/Subsurface-divelog/subsurface/issues/1607
and
https://github.com/Subsurface-divelog/subsurface/issues/1608

But maybe this will help others looking for massively large data files :-)

/D