plugins: minor tweaks

- add icon to PluginDialog
 - add icon to psbt_nosr
 - rename 'PSBT Nostr' as 'Nostr Multisig'

electrum/plugins/labels/manifest.json

@@ -1,6 +1,7 @@
 {
   "name": "labels",
   "fullname": "LabelSync",
+  "author": "The Electrum Developers",
   "description": "Save your wallet labels on a remote server, and synchronize them across multiple devices where you use Electrum. Labels, transactions IDs and addresses are encrypted before they are sent to the remote server.",
   "icon":"labelsync.png",
   "available_for": ["qt", "qml", "cmdline"]

electrum/plugins/psbt_nostr/manifest.json

@@ -1,8 +1,9 @@
 {
-  "name": "psbt_nostr",
-  "fullname": "PSBT over Nostr",
+  "name": "nostr_multisig",
+  "fullname": "Nostr Multisig",
   "description": "This plugin facilitates the use of multi-signatures wallets. It sends and receives partially signed transactions from/to your cosigner wallet. PSBTs are sent and retrieved from Nostr relays.",
   "author": "The Electrum Developers",
   "available_for": ["qt"],
+  "icon":"nostr_multisig.png",
   "version": "0.0.1"
 }