Limit application compute

[ChrisWellsWood]

In order to limit the amount of compute that a single user can use, I have added the following restrictions to the application:

1. A hard limit of 500 residues in a single structure file. As most of the algorithms do not scale linearly, the amount of compute required to calculate metrics increases steeply with the number of residues. 500 is bigger than most designed proteins.
2. A maximum of 30 structures can be loaded at a single time. This is to prevent user error as much as to limit the strain on the server. Previously, if the user tried to upload 1000 files, the application would have went along with that. Now the user must load files in batches of 30.
3. A timeout of 30 seconds has been added to the job queue to ensure that the queue isn't blocked by badly behaved jobs. I was tempted to limit this even further, so we need to keep an eye on the average job time.

Closes #26

[MichaelJamesStam]

This works really well! I did a test by trying to upload 400 antibody designs and the web server coped with it fine! Only 30 of them were processed and a lot of them were not ran because they exceeded the residue limit of 500.