Merge withdraw and kton into new transfer precompile

[boundless-forest]

In this PR, I merged the original withdraw precompile(0x15) and the kton precompile(0x16) into a new precompile contract, named transfer, which address is 0x15, the same as with the original withdraw precompile address.

Something important to notice:

I did not change the protocol of old precompiles. For application users who use kton precompile, just update the kton precompile address from 0x16 to 0x15. @hujw77 @sxlwar We should update wkton contract before this change goes to pangolin.

[hackfisher]

One question, does usize have the same byte length in different platforms? @AsceticBear @AurevoirXavier

[AurevoirXavier]

One question, does usize have the same byte length in different platforms? @AsceticBear @AurevoirXavier

https://matrix.to/#/!HzySYSaIhtyWrwiwEV:matrix.org/$162270534229674MqRiQ:matrix.org?via=matrix.parity.io&via=matrix.org&via=corepaper.org

[boundless-forest]

One question, does usize have the same byte length in different platforms? @AsceticBear @AurevoirXavier

Good questioin.

The answer from AurevoirXavier Element:

> bear | Darwinia Network
Can i use usize type for number in pallet?
> Xavier - Darwinia.Network
Yes
But in WASM it's u32
So make sure it won't be grow up to u32::max_value + 1

I also find some examples from substrate:

1. https://github.com/paritytech/substrate/blob/master/frame/authorship/src/lib.rs#L33
2. https://github.com/paritytech/substrate/blob/master/frame/elections/src/lib.rs#L153

In the end, I think this usage is ok.

[hackfisher]

@sxlwar please ACK these changes, might require companion PR in smart-app later.

[boundless-forest]

@AurevoirXavier Please review this pr again.