Demo

[looninho]

update pip packages, paths to demo datasets and minor changes

[looninho]

update package versions in requirement.txt and change its name to requireents.txt.
replace the ${PGPT_ROOT} by /PGPT in files concerned.

out of this repo, in your demo_detection.json, the dataset 024577_mpii_test doesn't exist. And in your demo_val.json the dataset becomes 024575_mpii_test so I have to remove this to run the demo properly.