Add SourceField and subclasses, rework Source
#1398
| Job | Run time |
|---|---|
| 1m 42s | |
| 2m 27s | |
| 1m 42s | |
| 2m 1s | |
| 2m 36s | |
| 2m 11s | |
| 6m 37s | |
| 2m 1s | |
| 1m 49s | |
| 2m 26s | |
| 2m 43s | |
| 3m 37s | |
| 2m 25s | |
| 2m 57s | |
| 3m 31s | |
| 3m 48s | |
| 4m 8s | |
| 4m 26s | |
| 53m 7s |