[R4R] #262 Fix tx search pagination

[ackratos]

Related issue: bnb-chain/node#262

tendermint change: bnb-chain/bnc-tendermint#12

tested with http://127.0.0.1:8080/txs?tag=tx.height=303&page=0&perPage=10000

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[darren-liu]

1. we should reject negative value
2. how should we handle if 2 31-digit number cannot hold all the txs, especially max per page is just 10000?

[ackratos]

2. how should we handle if 2 31-digit number cannot hold all the txs, especially max per page is just 10000?

Then the API user should pass page from 0 to 2^32 / 10000 and perPage always 10000 to get all txs.

Our usage is for explorer query txs in every block (by tag tx.height), which won't exceed 4000 (currently 1000) as our performance limitation.