[HyperKitty] #100: subject in threadview should be the most-used subject

[HyperKitty]

#100: subject in threadview should be the most-used subject
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Reporter:  sumanah      |      Owner:
    Type:  enhancement  |     Status:  new
Priority:  minor        |  Milestone:  1.2
 Version:               |   Keywords:  ui
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 When I am viewing a thread, if the subject line of the thread has changed
 and there are multiple possible subject lines, we should choose to display
 (at the top/title) the subject that the most messages used.