WebView deprecated on 10.14 and later #24

When compiling the FsprgEmbeddedStoreMac framework with a deployment target of 10.14 or later, Xcode outputs a list of deprecation warnings against WebView, such as:

FsprgEmbeddedStoreDelegate.h:61:18: warning: 'WebView' is deprecated: first deprecated in macOS 10.14 - No longer supported; please adopt WKWebView.
- (void)webView:(WebView *)sender didFailProvisionalLoadWithError:(NSError *)error forFrame:(WebFrame *)frame;

The framework should be updated to use WKWebView before Apple drops support for WebView altogether.