-Added DefaultExistingRowsTo fluent command when creating columns for existing tables.
-Added a ColumnExpressionBuilderHelper to centralise some of the duplicated functionality in the Column related Expression Builders.
-Added VS2013 solution file
-Refactored Unique Column common logic into shared ColumnExpressionBuilderHelper class, refactored tests.
-Removed any reference to ExistingRowDefault, renamed to SetExistingRowsTo, to address confusion with this being related to db engine defaults.
-Refactored Indexed() call out of individual column expression builders into central location.
Merge pull request #462 from mstancombe/master

  -Refactored Indexed() call out of individual column expression builders into central location.
  -Removed any reference to ExistingRowDefault, renamed to SetExistingRowsTo, to address confusion with this being related to db engine defaults.
  -Refactored Unique Column common logic into shared ColumnExpressionBuilderHelper class, refactored tests.
  -Added DefaultExistingRowsTo fluent command when creating columns for existing tables. -Added a ColumnExpressionBuilderHelper to centralise some of the duplicated functionality in the Column related Expression Builders. -Added VS2013 solution file