Enhance SQL Event Store Creation

Added schema test to EXISTS queries in Ncqrs.Eventing.Storage.SQL.TableCreationScript.sql that wrap table & index creation.

Added Ncqrs.Eventing.Storage.SQL.ConstraintCreationScript.sql to the Ncqrs project, and moved CONSTRAINT creation from Ncqrs.Eventing.Storage.SQL.TableCreationScript.sql to Ncqrs.Eventing.Storage.SQL.ConstraintCreationScript.sql.

Modified Ncqrs.Eventing.Storage.SQL.MsSqlServerEventStore to run TableCreationScript.sql and then ConstraintCreationScript.sql when InitializeEventStore() is called.

Sorted the constants in Ncqrs.Eventing.Storage.SQL.Queries

Updated Samples/MyNotes/README.md for correctness, grammar, and spelling.

Updated Samples/MyNotes/MyNotesReadModel.sql for readability

Updated Samples/MyNotes/MyNotesEventStore.sql to put it in line with Ncqrs.Eventing.Storage.SQL.TableCreationScript.sql