Add option for composing emails in plain text format. see #350

_locales/en/messages.json

@@ -1270,5 +1270,13 @@
   "CORS_give_allurls_perm": {
     "message": "Give \"all URLs\" permission",
     "description": ""
+  },
+  "prefs_OptionText_composing_plain_text": {
+    "message": "Composing in plain text",
+    "description": ""
+  },
+  "prefs_OptionText_composing_plain_text_Info": {
+    "message": "Check this option if you're composing the emails in plain text format.",
+    "description": ""
   }
 }

options/mzta-options-default.js

@@ -22,6 +22,7 @@ export const prefs_default = {
     chatgpt_win_width: 700,
     default_chatgpt_lang: '',
     default_sign_name: '',
+    composing_plain_text: false,
     connection_type: 'chatgpt_web',     //Other values: 'chatgpt_api', 'ollama_api', 'openai_comp_api', 'google_gemini_api'
     chatgpt_web_model: '',
     chatgpt_web_tempchat: false,

options/mzta-options.html

@@ -101,6 +101,17 @@
           </label>
         </td>
       </tr>
+      <tr>
+        <td><label>
+          <span>__MSG_prefs_OptionText_composing_plain_text__</span>
+        </label></td>
+        <td>
+          <label>
+            <input type="checkbox" id="composing_plain_text" name="composing_plain_text" class="option-input" />
+            &nbsp;<span>__MSG_prefs_OptionText_composing_plain_text_info__</span>
+          </label>
+        </td>
+      </tr>
       <tr>
         <td>
           <label>