Adding more FormSignature tests. Proves 2. of #998.
Fixing test where FormSignature would fail on fields.

Fixes 2. of issue #998.

Refactoring into symmetric compile/parse methods.
Adding test for security helper sending correct signature fields.
Make excluded fields part of form signature.
Fix form signature where locked would be included in fields.
Merge pull request #1137 from davidpersson/bug/form-sign-fixes

Multiple form signing fixes