Certificate UI/Import (#798)

* Sketching out.

* WIP

* WIP

* Dump

* Apply stash

* Merge + WIP

* UI

* More WIP

* Agent config

* UI cleanup

* Restore dirty files

* XPC

* Edit/delete

* UI fixes

* Cleanup

* Change id for OpenSSHCertificate to hex of md5

* Fix runtime warning for confirmation dialog

* Mark strings as reviewed

* Cleanup

* Fix agent tests

Sources/Secretive.xcodeproj/xcshareddata/xcschemes/Secretive.xcscheme

@@ -23,7 +23,7 @@
       </BuildActionEntries>
    </BuildAction>
    <TestAction
-      buildConfiguration = "Test"
+      buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES">