Implement endpoints for token module

[nagdahimanshu]

Description

Implement endpoints for token module There is need to implement similar endpoint like getTotalSupply to retrieve stakedLSK, inflationRate and totalSupplyLSK This information can be included in blockchain application stats endpoint response by lisk-service.

Endpoints:

• getStakedLSK
• getInflationRate
• totalSupplyLSK

Acceptance Criteria

• Suggested endpoint is added to token module
• Add unit test for all the endpoints