Feature Request: Scroll lock panels

[kba]

When comparing PAGE-XML and, to a lesser extent, zoomed in images, It would be neat if one could link two panels (e.g. by clicking on a lock symbol in the panel's toolbar), so that scrolling in one would scroll the other one automatically.

For a purely textual comparison, dinglehopper or a future diff-view (#13) is best but I sometimes use it to compare things like the generated IDs of elements or to spot if any text is missing or not consistent across TextEquiv levels and not having to scroll two panels manually would help.