Add functionality to wallets with only stake keys

[dostrelith678]

Not sure what you guys think of this - might be a bit stretched out.

Right now, if you remove payment keys from a cli wallet, it will be deemed unavailable for delegating/pledging:

>> FUNDS >> DELEGATE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Online mode  -  The default mode to use if all keys are available

Hybrid mode  -  1) Go through steps to build a transaction file
                2) Copy built tx file to offline computer
                3) Sign it using 'Sign Tx' with keys on offline computer
                   (CNTools started in offline mode '-o' without node connection)
                4) Copy the signed tx file back to online computer and submit using 'Submit Tx'

Selected value: [o] Online

# Select wallet to delegate
WARN: No wallets available that can be delegated or used as pool pledge/owner/reward wallet!

Ideally, they should still be usable if there is another wallet available for paying the fees.

[Scitz0]

This could be a future enhancement of CNTools. Right now it uses the same wallet for paying the transaction fee. This is not just for delegating either, same goes for pledge wallet and other options.

But I can see cases where it would beneficial to be able to select a separate wallet to pay for transaction and deposit fees.

[rdlrt]

Need to be slightly careful with this requirement now, given that we support single-address from HD Wallets (Daedalus/Yoroi) and ledger devices. This could break the wallet functionality for such wallets