Add a way to limit deserialized string lengths

and use it for most strings being serialized.

Rebased-From: 216e9a4
From Bitcoin a78996: Limiting deserialized string lengths. Tested by artificially shortening alert.h LimitedString lengths to 4,
and running the alert_tests unit test. Truncated alerts to 4 like we wanted.
From Bitcoin a78996: Limiting deserialized string lengths. Tested by artificially shortening alert.h LimitedString lengths to 4, and running the alert_tests unit test. Truncated alerts to 4 like we wanted.
Merge pull request #695 from michilumin/1.8.1-dev-string-length

1.8.1 dev string length