encode label id in string index

[javeme]

Change-Id: Ia7c1be49c740a654dd687a79686a1044be10bd1f

[codecov]

Codecov Report

Merging #894 into master will increase coverage by 0.02%.
The diff coverage is 89.18%.

@@             Coverage Diff              @@
##             master     #894      +/-   ##
============================================
+ Coverage     72.23%   72.25%   +0.02%     
- Complexity     4487     4497      +10     
============================================
  Files           287      287              
  Lines         21411    21438      +27     
  Branches       3017     3025       +8     
============================================
+ Hits          15467    15491      +24     
- Misses         4432     4433       +1     
- Partials       1512     1514       +2     

Impacted Files	Coverage Δ	Complexity Δ
...u/hugegraph/backend/serializer/TextSerializer.java	86.57% <ø> (ø)	88.00 <0.00> (ø)
.../backend/store/memory/InMemoryDBStoreProvider.java	100.00% <ø> (ø)	11.00 <0.00> (ø)
...java/com/baidu/hugegraph/schema/SchemaElement.java	79.31% <ø> (-0.36%)	26.00 <0.00> (-1.00)
...egraph/backend/store/hbase/HbaseStoreProvider.java	100.00% <ø> (ø)	6.00 <0.00> (ø)
...egraph/backend/store/mysql/MysqlStoreProvider.java	100.00% <ø> (ø)	6.00 <0.00> (ø)
...kend/store/postgresql/PostgresqlStoreProvider.java	92.10% <ø> (ø)	5.00 <0.00> (ø)
...ph/backend/store/rocksdb/RocksDBStoreProvider.java	100.00% <ø> (ø)	6.00 <0.00> (ø)
...du/hugegraph/backend/tx/GraphIndexTransaction.java	79.75% <75.00%> (-0.10%)	185.00 <0.00> (ø)
...hugegraph/backend/serializer/BinarySerializer.java	83.30% <81.25%> (-0.09%)	104.00 <4.00> (ø)
...va/com/baidu/hugegraph/backend/id/IdGenerator.java	82.20% <100.00%> (ø)	19.00 <0.00> (ø)
... and 10 more

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[javeme]

removed big id since:
hugegraph@1208522#diff-a7d694d773f6542d375ed1a42eb89f6dR349
hugegraph@efcd839#diff-a7d694d773f6542d375ed1a42eb89f6dR340