Handle P2PK addresses

[martinboehm]

There is an issue (caused by the design decision in Blockbook) with pay to public key addresses P2PK: bitcoin type coins in Blockbook use public key scripts, not addresses (as the value returned by by the abstraction bchain.AddressDescriptor from parsers) to index data. When searching for an address in explorer, Blockbook must convert the address to the script before the lookup.
The problem with P2PK address is that it is the same as pay to public key hash, but has different script (which cannot be obtained from the address). Blockbook therefore does not find the transactions of P2PK address and also computes balances of P2PK and P2PKH separately, with different results than returned some other explorers.

Fortunately there is a way how to change this behavior: detect in the parser.GetAddrDescFromVout and parser.GetScriptFromAddrDesc P2PK script and convert it to P2PKH script.

[martinboehm]

P2PK scripts are converted to P2PKH address descriptors so that P2PK and P2PKH are indexed together. Existing databases must be reindexed for the feature to work.