Mono BlockingCollection workaround.

Mono up to version 3.11 has issues with BlockingCollection.
It returns null on TryTake (success).
On Unix default to no pool.

Changed DB pool size default (use cpu count instead of 20)
Security changes.

Security dsl should keep password cache instead of actual password.
Default to hash password comparison.
Dont convert SecureString to string.
Support for nullable secret field.
Unit of work pattern added to Revenj.Core

Since Revenj core should be used as a library, expose simple way to create and conusme transactions.
Latest Json.NET. Wcf setup simplified.

Removed custom Json.NET; added converter to simulate customization.
Wcf config changed to disable permissions by default.
GeneratedModel.dll recompiled due to various dependency changes.