New routes

[scottinet]

• added the getServerInfo API route
• added the listIndexes API route
• added a new index optional argument to the listCollections method. If no index is provided, takes the kuzzle.defaultIndex instead. If no default index is found, throw an error.

[codecov-io]

Current coverage is 100.00%

Merging #40 into master will not affect coverage as of cc3995c

@@            master     #40   diff @@
======================================
  Files            5       5       
  Stmts          794     824    +30
  Branches       198     204     +6
  Methods          0       0       
======================================
+ Hit            794     824    +30
  Partial          0       0       
  Missed           0       0       

Review entire Coverage Diff as of cc3995c

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