Implement post editing functionality for Mastodon

Add ability to edit posts in Mastodon with full support for:
- Editing post text and content warnings
- Re-uploading or keeping existing media attachments
- Editing poll options (for posts with polls)
- Modifying visibility and language settings
- All features available through web interface

Changes:
- Add edit_post() method in Mastodon session to handle API calls
- Create editPost dialog class that loads existing post data
- Add edit_status() method to buffer controllers
- Add Edit menu item to base and notification menus
- Register edit_post action in all keymaps (no default key assigned)
- Add edit_post() action handler in main controller

The edit option is only enabled for the user's own posts (not boosts).
Users can access the feature through the context menu or by assigning
a keyboard shortcut in the keymap editor.

src/wxUI/dialogs/mastodon/menus.py

@@ -8,6 +8,8 @@ class base(wx.Menu):
         self.Append(self.boost)
         self.reply = wx.MenuItem(self, wx.ID_ANY, _(u"Re&ply"))
         self.Append(self.reply)
+        self.edit = wx.MenuItem(self, wx.ID_ANY, _(u"&Edit"))
+        self.Append(self.edit)
         self.fav = wx.MenuItem(self, wx.ID_ANY, _(u"&Add to favorites"))
         self.Append(self.fav)
         self.unfav = wx.MenuItem(self, wx.ID_ANY, _(u"R&emove from favorites"))
@@ -36,6 +38,8 @@ class notification(wx.Menu):
             self.Append(self.boost)
             self.reply = wx.MenuItem(self, wx.ID_ANY, _(u"Re&ply"))
             self.Append(self.reply)
+            self.edit = wx.MenuItem(self, wx.ID_ANY, _(u"&Edit"))
+            self.Append(self.edit)
             self.fav = wx.MenuItem(self, wx.ID_ANY, _(u"&Add to favorites"))
             self.Append(self.fav)
             self.unfav = wx.MenuItem(self, wx.ID_ANY, _(u"R&emove from favorites"))