Changes to WateGate client:
-implemented user management
-some ui fixes(like forms visible buttons, ability to sign in using Enter key)
-fixed bug from last commits when there was no event attached for CellContentClick in mainDataGridView.
Changes to StaticValuesDll:
-added user management to Service interface (IWaterGateService).
Changes to Service:
-added user management to Repository and WaterGateService.