Let HugeTraverser.topN() support template Key

[javeme]

Change-Id: I40cf6583d1c3e7303237933b39d77f2139679e93

[codecov]

Codecov Report

Merging #949 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #949      +/-   ##
============================================
+ Coverage     71.78%   71.80%   +0.01%     
+ Complexity     4676     4675       -1     
============================================
  Files           298      298              
  Lines         22377    22377              
  Branches       3176     3176              
============================================
+ Hits          16064    16068       +4     
+ Misses         4732     4729       -3     
+ Partials       1581     1580       -1     

Impacted Files	Coverage Δ	Complexity Δ
...du/hugegraph/backend/tx/GraphIndexTransaction.java	79.45% <0.00%> (-0.13%)	186.00% <0.00%> (ø%)
...a/com/baidu/hugegraph/backend/query/Condition.java	79.67% <0.00%> (+0.40%)	31.00% <0.00%> (ø%)
...om/baidu/hugegraph/api/filter/ExceptionFilter.java	66.66% <0.00%> (+4.30%)	0.00% <0.00%> (ø%)

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