Fix #17: Computer Name Template Cache

Correctly invalidates the Expression Cache when a Computer Name Template
changes.

Disco.Web/Areas/API/Controllers/DeviceProfileController.cs

@@ -221,6 +221,8 @@ namespace Disco.Web.Areas.API.Controllers
             deviceProfile.ComputerNameTemplate = ComputerNameTemplate;
 
             dbContext.SaveChanges();
+
+            deviceProfile.ComputerNameInvalidateCache();
         }
 
         private void UpdateDefaultOrganisationAddress(Disco.Models.Repository.DeviceProfile deviceProfile, string DefaultOrganisationAddress)