Introduce address exclusion in `platform.exportAVAX` and other platform APIs.

[arijitAD]

Describe the bug
Over time an account might have to manage p-chain multiple addresses since it uses the UTXO model. It will be helpful if there is field in exportAVAX API where we can also exclude an address.

Current API:

platform.exportAVAX(
    {
        amount: int,
        from: []string, //optional
        to: string,
        changeAddr: string, //optional
        username: string,
        password: string
    }
) -> 
{
    txID: string,
    changeAddr: string
}

Expected:

platform.exportAVAX(
    {
        amount: int,
        from: []string, //optional
        excludeAddr: []string, //optional
        to: string,
        changeAddr: string, //optional
        username: string,
        password: string
    }
) -> 
{
    txID: string,
    changeAddr: string
}

[StephenButtolph]

The node APIs are designed as simple convenience methods. To improve generality and security, it is recommend to use a wallet service that does not require keys to be placed onto a running node.