restyle page-edit button to fixed position when text scrolled

[finanalyst]

• if an edit is needed, now there is no need to scroll to top of file
• move the div to the main tile
• restyle to make fairly unobtrusive
• z-index so it floats above text.
• opacity 50% so when overlapping, text is visible

[finanalyst]

@coke this is to make it easier to access the editing button.

[finanalyst]

Test deployment is live at new-raku, eg operators May need to refresh browser cache to get the new CSS for the edit button