Swift 5, beginning of Tests, fixes, and improvements!

Summary:

• Library upgraded to Swift 5
• Introduction of tests to reduce regression and make the library more bullet proof.
• Sorting arrow colour can be customised now in the configuration object.
• Fix: Using a specific initialiser would ignore DataTableConfiguration leading to custom configurations not being used.

Technical:

• The swift language has been upgraded to swift 5
• A test target has been added, with an initial tests to ensure initialisation with custom configuration works for a specific initialiser that would previously not initialise with the configuration object.
• The SwiftDataTableConfiguration and DataTableColumnOrder models now conforms to Equatable
• The sorting arrow icons now render as template mode enabling a custom colour.