Renames signals for consistency

Updates signal names across UI components (checkbox, textbox, and CAN) to use more consistent and descriptive names, improving code readability and maintainability. The 'on_change' and 'on_send' signals are renamed to 'changed' and 'send' respectively.

UI/ui_checkbox.cpp

@@ -18,14 +18,14 @@ void UI_checkbox::click()
 {
     m_checked = !m_checked;
     emit ui_changed();
-    emit on_change(m_checked);
+    emit changed(m_checked);
 }
 
 void UI_checkbox::set_state(bool state)
 {
     m_checked = state;
     emit ui_changed();
-    emit on_change(m_checked);
+    emit changed(m_checked);
 }
 
 bool UI_checkbox::state() const