Save webdirurl in database and fixes #4351

Currently only webdirurl is saved in database, and it is not used anywhere.  Need final decision how we use it and reduce load of `condor_q` command to schedd.

Also Dagman ClassAd has `CRAB_RestTaskUrl` and `CRAB_RestTaskInstance` which can be used for uploading together to ASO couch document to solve DBS publication issue.
```
CRAB_RestTaskUrl = balcas-crab.cern.ch
CRAB_RestTaskInstance = /crabserver/{dev|prod|preprod}/
```
Also fixed this https://github.com/dmwm/CRABServer/issues/4351. Now sandbox can be found in web directory to speed up debugging.

Signed-off-by: Justas Balcas <juztas@gmail.com>