Remove unnecessary calls to get an external IP

* Skip call to get an external IP address if one is already specified
in the [NETWORK] configuration or the IP address has already been
determined previously
  ( This will also considerably speed up startup )
  - Utilities: add public static string HostName that is set when the
configuration is read
  - SimulationBase & MinimaSimulationBase
      - only get an external IP address (dyndns call) is no
configuration has been specified
Issue #13 - excess index length causing crashes

* Add a length specifier to the MySql table index definition so that
long fields can be have indexes defined as not using the full field
length
    ( Issue #13 - passwordHash causing a crash when creating auth table)
  - MySQLDataManager.CreateTable - added processing for the additional
IndexSize specification
  - Migrator - Added additional override to allow for size
specification of index field
  - IDataConnector - Added additional IndexSize parameter to the index
definition
  - AuthMigrator_5 - added a 255 length specifier to the "passwordHash"
index
  - AgentMigrator_4 - added a 255 length specifier to the "Keyword"
index