Abstract out SignatureChecker
Make signature cache optional
Replace SCRIPT_VERIFY_NOCACHE by flag directly to checker
Don't translate state.Abort() messages

There is only one message passed to AbortNode() that makes sense to
translate to the user specifically: Disk space is low. For the others
show a generic message and refer to debug.log for details.

Reduces the number of confusing jargon translation messages.
Update English translation
Merge pull request #4890

e790c37 Replace SCRIPT_VERIFY_NOCACHE by flag directly to checker (Pieter Wuille)
5c1e798 Make signature cache optional (Pieter Wuille)
c7829ea Abstract out SignatureChecker (Pieter Wuille)
Merge pull request #5036

eb6b3b2 Update English translation (Wladimir J. van der Laan)
b9b2e3f Don't translate state.Abort() messages (Wladimir J. van der Laan)