console: grideditor - re-add column headers

Also remove special-case shortcut for user-agent. This is awkward in the new
structure. Down the track we can come up with a more regular mechanism like
snippets.

mitmproxy/tools/console/grideditor/base.py

@@ -309,7 +309,8 @@ class BaseGridEditor(urwid.WidgetWrap):
 
         self.walker = GridWalker(self.value, self)
         self.lb = GridListBox(self.walker)
-        w = urwid.Frame(self.lb)
+        w = urwid.Frame(self.lb, header=h)
+
         super().__init__(w)
         signals.footer_help.send(self, helptext="")
         self.show_empty_msg()

mitmproxy/tools/console/grideditor/editors.py

@@ -39,7 +39,6 @@ class HeaderEditor(base.FocusEditor):
             urwid.Text([("text", "Special keys:\n")])
         ]
         keys = [
-            ("U", "add User-Agent header"),
         ]
         text.extend(
             common.format_keyvals(keys, key="key", val="text", indent=4)
@@ -48,25 +47,6 @@ class HeaderEditor(base.FocusEditor):
         text.extend(h)
         return text
 
-    def set_user_agent(self, k):
-        ua = user_agents.get_by_shortcut(k)
-        if ua:
-            self.walker.add_value(
-                [
-                    b"User-Agent",
-                    ua[2].encode()
-                ]
-            )
-
-    def handle_key(self, key):
-        if key == "U":
-            signals.status_prompt_onekey.send(
-                prompt="Add User-Agent header:",
-                keys=[(i[0], i[1]) for i in user_agents.UASTRINGS],
-                callback=self.set_user_agent,
-            )
-            return True
-
 
 class RequestHeaderEditor(HeaderEditor):
     title = "Edit Request Headers"