Implemented an up vote(like) system for the blog comments#111

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TonyXia2001 wants to merge 3 commits intoucladevx:masterfrom TonyXia2001:upvote-done

+92-8

Commits on May 7, 2020

fixed a bug in mentor search. The mentor search result no longer depends on the order of the words in the search query. Moreover, duplicates are removed from the result as well.
TonyXia2001
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Commits on May 27, 2020

completed the upvote system for the blogs
TonyXia2001
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Commits on Jun 4, 2020

merged upstream repo
TonyXia2001
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