Add SourceField and subclasses, rework Source
#1397
| Job | Run time |
|---|---|
| 10m 36s | |
| 2m 2s | |
| 2m 14s | |
| 2m 21s | |
| 2m 19s | |
| 2m 38s | |
| 1m 33s | |
| 1m 34s | |
| 2m 20s | |
| 1m 38s | |
| 1m 49s | |
| 2m 20s | |
| 1m 39s | |
| 3m 32s | |
| 3m 3s | |
| 3m 7s | |
| 4m 23s | |
| 3m 13s | |
| 52m 21s |