Merge sibling fix

[shresthabijay]

fixes #816

[shresthabijay]

@raineorshine The issue was the oldValue was not being updated after the thoughtsRanked being accessed from props was updated. Since thoughtChangeHandler checks if the oldValue has any associated thought using getThought, it prevented dispatching exisitingThoughtChange. I made the necessary changes to fix it. Apart from that I have made some changes to the ContentEditable to use isEditing to track focus state instead of using document.activeElement which was not reliable between re-renders. Please test the changes. Thanks!

[raineorshine]

Thanks for the quick turnaround! Works great.