Modified SqlServerStorage to accept name of a connectionstring

Moved GetConnectionStringToUse -method from
SqlServerMessageQueueConfigurationExtension to a new
ConnectionStringUtil-class in Shared -namespace so it also usable from
SqlServerStorage -class.

Modified SqlServerStorage to accept name of a connectionstring in
addition to an actual connectionstring.

Modified the name of the parameter in the constructor of
SqlServerStorage to reflect new behaviour. Also modified the parameter
names in class inheriting from SqlServerStorage.