Added tests
Implemented Repository

Decided to go with a repository pattern to try and centralise the query
logic.
Updated to implement repository pattern
New method to check for arbs for single fixture
Added UpdateArb method

Replaced overly complex method with a method that can be used to
specifically check if an arb represents the latest odds available in the
database and prompt an update if the data is found to be out-dated.
Added tests for new method and updated a helper method.
Renamed some files and folders