fix: let fromHeight of 0 mean the latest block instead of the genesis…

[niklr]

What kind of change does this PR introduce? (check at least one)

• Improvement
• Bugfix
• Feature
• Refactor
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

Current dapps or scripts could break if they assume startHeight = 0 will return all events since genesis block.

[niklr]

Solves #579 partially.

[viteshan]

This modification will cause confusion to users who are currently using it.

[niklr]

Both RPC methods ledger_getVmLogsByFilter and subscribe_getLogs have been extended with the optional pageIndex and pageSize pagination parameters. It can be tested as follows:

let logs = await provider.request("ledger_getVmLogsByFilter",
  {
    "addressHeightRange": {
      [a.address]: {
        "fromHeight": "1",
        "toHeight": "0"
      }
    },
    pageIndex: 1,
    pageSize: 6
  });

I have to say I'm not a fan of those changes. Instead we should just abort the request (return error in for loop) if a certain time limit (e.g. >=3000ms) is exceeded. What do you think @charles-liu @viteshan?