Add dynamic timeout on pdfalto_server

[lfoppiano]

This PR should add a dynamic timeout on the pdfalto_server script using the argument --timeout XY. #923

It also avoid changing the virtual memory on mac Os. #894

[coveralls]

Coverage increased (+0.008%) to 39.963% when pulling 6fd7d19 on feature/timeout_pdfalto_server into e06acf4 on master.

[kermitt2]

Thanks a lot Luca !

I tested on Linux 64, but not with Mac Os, and it works fine!

Note that it breaks compatibility of grobid-home version 0.7.1 when running version 0.7.2-SNAPSHOT, grobid-home will need to be up-to-date too, but there's no other way to make that happen.