Stop plist editor from randomly jumping scroll position on row add

[chrisgrande]

Fixes issue where the plist editor would randomly jump scroll position when adding new rows towards the bottom of the editor.

[chrisgrande]

Nevermind - this only mitigated an issue with adding rows to dicts that was jumping the editor around.

I see what you're saying when adding a new item all the way at the bottom under Details and it jumping to the top. I think I see what's going on but it will take a bit more kicking.

[chrisgrande]

eb61d4c will auto select the new key when added.

[gregneagle]

Looks great!