Make Portable App also a Silent App

Fixes two portable app bugs, to make the app fully "silent", not just
"portable". This means that not only are all data files stored in the
"Portable Settings" folder, but the app should leave no trace on the
host system.

- Disable Electron's single instance mode so no lock file is created in
"%APPDATA%\Roaming\WebTorrent".

- Put Electron crash files, and other electron files into the "Portable
Settings\Temp" folder instead of "%APPDATA%\Temp".

src/config.js

@@ -116,9 +116,7 @@ function getConfigPath () {
 }
 
 function getDefaultDownloadPath () {
-  if (!process || !process.type) {
-    return ''
-  } else if (IS_PORTABLE) {
+  if (IS_PORTABLE) {
     return path.join(getConfigPath(), 'Downloads')
   } else {
     return getPath('downloads')
@@ -126,9 +124,14 @@ function getDefaultDownloadPath () {
 }
 
 function getPath (key) {
-  if (process.type === 'renderer') {
+  if (!process.versions.electron) {
+    // Node.js process
+    return ''
+  } else if (process.type === 'renderer') {
+    // Electron renderer process
     return electron.remote.app.getPath(key)
   } else {
+    // Electron main process
     return electron.app.getPath(key)
   }
 }
@@ -159,6 +162,7 @@ function isPortable () {
 
 function isProduction () {
   if (!process.versions.electron) {
+    // Node.js process
     return false
   }
   if (process.platform === 'darwin') {