Remember scroll & cursor position even on files not in the working set

[peterflynn]

Steps:

1. Single-click a file to open it
2. Scroll to the bottom
3. (optional) Select some text
4. Open a different file
5. Click back to the original file

Result:
Scroll position and cursor position / selection were lost, because the file wasn't in the working set.

Expected:
We should maintain the basic scroll and cursor position state for any document that is opened. Espresso, the closest analog to our UI design, does this.

(Espresso actually remembers this state even after the project has been saved, for all files that have been viewed. If we want to go that far I think it should either be a 2nd bug or a full-blown user story).

[jlondon]

Recommending for Sprint 4 Bug Fix Story

[jlondon]

Moving to the Product Backlog as a user story so removing Sprint 4 label. Adam will close this out once in the backlog.

[jlondon]

Moved to backlog - closing