Apply validator flags from testdata.yaml

[thorehusfeldt]

Read flags for validators from testdata.yaml, such as

input_validator_flags:
  format_validator: case_sensitive
  topology: --max_connected_components 1
output_validator_flags: float_tolerance 1e-5
---
input_validator_flags: min_n 100 max_n 1000

and apply them correctly.

Interesting details that need to be kept in mind:

• [x] Input validators can (but don’t have to) be specified by validator name
• [x] There are inheritance rules (the closest applicable parental flags “win”)
• [x] The empty string are valid flags (relevant for inheritance)
• [x] Flags apply to included testcases at the point of their inclusion (rather than their origin)
• [x] Answer validators use output validator flags