Add Benchmarks, Blocks, and Miners API

[DalmationCadet]

No description provided.

[crackfoo]

Can you adjust the blocks api to only list visible coins/blocks?

[crackfoo]

Also, if you have rentals enable you get this error in the blocks api:

Internal Server Error
Undefined offset: 0

[crackfoo]

REQUEST_URI=/api/blocks
2018/06/11 12:28:25 [error] [php] Undefined offset: 0 (/home/next/web/yaamp/modules/api/ApiController.php:425)
Stack trace:
#0 /home/next/web/framework/web/CController.php(286): ApiController->runAction()
#1 /home/next/web/framework/web/CController.php(265): ApiController->runActionWithFilters()
#2 /home/next/web/framework/web/CWebApplication.php(304): ApiController->run()
#3 /home/next/web/framework/web/CWebApplication.php(141): CWebApplication->runController()
#4 /home/next/web/framework/base/CApplication.php(185): CWebApplication->processRequest()
#5 /home/next/web/index.php(27): CWebApplication->run()
REQUEST_URI=/api/blocks
~

[tpruvot]

not wanted