Used `sby --autotune` to find other engines which fail (though there aren't any other exceptions that I could find).
Parse errors from `abc bmc3` and `abc sim3` instead of returning UNKNOWN.
- Status database only gets called from summary events instead of from engines.
- More trace witnesses (.aiw and .yw) are tracked as events.
- Multiple tracefiles can be included in the same trace summary, varying only by
extension. These are ordered by priority so that in the logfile only a single
tracefile is listed.
- For engines where multiple properties can be collected for a single trace,
these properties are now available for all traces until the next step. If any
properties are collected but never recorded with a trace, an error is raised.
- Fix formatting for events without steps (e.g. running abc with `vcd off`).
- Drop task_property_data table entirely, since it is now redundant and unused.
- Fix properties being skipped in all status dump if they don't have a trace.
ABC will sometimes return negative frame numbers when proving by convergence, e.g.
```
engine_0: Proved output 1 in frame -698905656 (converged).
engine_0: Proved output 4 in frame -698905656 (converged).
```
This change fixes these properties being missed and causing the engine status to return UNKNOWN due to `proved_count != len(proved)`.
