Fix console scroll - comment on how scrolling works (#1448)

* Force console scroll area to be multiple of line height. Tons of comments.
* Resize POCSAG console to fill height.
* Make scoll behavior comment clearer

firmware/common/ui_widget.hpp

@@ -332,8 +332,8 @@ class Console : public Widget {
     void on_hide() override;
 
    private:
-    // bool visible = false;
     Point pos{0, 0};
+    Dim scroll_height = 0;
     std::string buffer{};
     static bool scrolling_enabled;