Refactor: GeoCoder closes the DbConnection

Responsibility for closing the db connection moved from the caller to
the GeoCoder to enable easier use by other applications.
IGeoCoder: now inherits IDisposable
Program: Connection initialisation and close moved to GeoCoder
GeoCoder: now responsible for closing the db connection on disposal
FormGazetteer: now responsible for creating and disposing the GeoCoder
MatchProvider: connection now private
UI: Open file dialog default to desktop removed
UI: Bug fixes

FormLoadInput: Input filename text not now cleared if user cancels
selection
FormLoadInput: Wait cursor displayed during input file load
Bug fix: Un-coded lines now showing correctly

InputData: An un-coded line is now defined as one with a name but no
code
UI bug fix: Match-All must be run before manual match