change_instructions_navigator_1.xsl: UI improvements
Order of the links analogous to the Java implementation: first, prev, current instruction count, next, last (so they're like a timeline). If possible, have the navigation links always stay on top of the page, even if the user scrolls. If possible, make the scrollbar jump to the place where an instruction/operation did take place when clicking on the navigation links. The header also needs a viewport specified for mobile.