preliminary google crashpad integration

First attempt at automated out-of-process crash reporting. Have only
updated AppVeyor script so far, so if this works (which it won't), it'll
only work on Windows.

app/common/crashpadinterface.h

@@ -0,0 +1,34 @@
+/***
+
+  Olive - Non-Linear Video Editor
+  Copyright (C) 2019 Olive Team
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
+#ifndef CRASHPAD_INTERFACE_H
+#define CRASHPAD_INTERFACE_H
+
+#ifdef USE_CRASHPAD
+
+#include <client/crashpad_client.h>
+#include <client/crash_report_database.h>
+#include <client/settings.h>
+
+bool InitializeCrashpad();
+
+#endif // USE_CRASHPAD
+
+#endif // CRASHPAD_INTERFACE_H