settings: pasting private key should update pubkey

If the user pastes a private-key and the pubkey input is empty,
it should be ok to generate and autofill the pubkey field without
confusing the user. There might be circumstances where it is
preferred to see an error if the pubkey does not correspond with
the private key.

Added an on paste event listener that tries to generate and auto-
fill the pubkey (if empty).

src/main.js

@@ -579,6 +579,13 @@ importBtn.addEventListener('click', () => {
 });
 
 settingsForm.addEventListener('input', () => validKeys(privateKeyInput.value, pubKeyInput.value));
+privateKeyInput.addEventListener('paste', (event) => {
+  if (!pubKeyInput.value && event.clipboardData) {
+    try {
+      pubKeyInput.value = getPublicKey(event.clipboardData.getData('text'));
+    } catch(err) {} // ignore as the error will be shown by validKeys later on input
+  }
+});
 
 function validKeys(privatekey, pubkey) {
   try {