Improve help messages

[camembera]

1. The default help for beacond has this line as the first line of output:
   "A basic beacon node, usable most standard networks."
   maybe: "A beacon node, usable with most Ethereum execution clients"

2. help deposit create-validator says: Creates a validator deposit with the necessary credentials. This suggests it transacts for you. The help further refers to a broadcast flag, which is not otherwise mentioned. Revise to clarify what this command now does, which is generate transaction parameters.

3. deposit validate should produce some kind of message to indicate that the parameters check out. Right now the only hint everything's fine is if the exit status $? is 0

4. deposit create-validator returns the amount as a hex string. If you then provide this hex string to deposit validate it is rejected. Either return decimal (preferred) or accept hex (misleading, because this is generally understood to represent bytes and not a hexademical encoding of a decimal number).

[wonderfan]

Thanks for your feedback and let me refine them.

[wonderfan]

./build/bin/beacond 
A basic beacon node, modular and PoL chain usable with most Ethereum execution clients.