Apply additional security recommendations (#2050)

* enable sandbox

* enable CSP (umami tentatively works?) and reduce amount of ipc APIs exposed

* remove csp from index

src/main/env.ts

@@ -0,0 +1,15 @@
+export const disableAutoUpdates = () => {
+    return process.env['DISABLE_AUTO_UPDATES'];
+};
+
+export const isMacOS = () => {
+    return process.platform === 'darwin';
+};
+
+export const isWindows = () => {
+    return process.platform === 'win32';
+};
+
+export const isLinux = () => {
+    return process.platform === 'linux';
+};