Expose ed25519 key explicitly and remove admin_key in t_entities

[mike-burrage-hedera]

Detailed description:

key column will now be used in place of admin_key where admin_key was used in the past. No entity had both

• copied data from t_entities.admin_key to t_entities.key if present
• deprecated t_entities.admin_key
• added t_entities.ed25519_public_key_hex (lowercase hex string if the key)
• updated java, sql function, and rest-api for this change
• rest-api will no longer be returning admin_key publicly (didn't make sense on accounts anyway)

Which issue(s) this PR fixes:
Fixes #56

Special notes for your reviewer:

Checklist

• Documentation added
• Tests updated

[gregscullard]

Oddly I was thinking about the same thing last night !

See suggested changes, would also suggest adding a unit test including a valid key in upper case to test it comes out of utility.protobufKeyToHexIfEd25519OrNull in lowercase.

[mike-burrage-hedera]

Can't have a unit test where utility.protobufKeyToHexIfEd25519OrNull() produces uppercase, since it always produces lowercase, but I updated the javadoc on it to make that explicit.

[gregscullard]

Can't have a unit test where utility.protobufKeyToHexIfEd25519OrNull() produces uppercase, since it always produces lowercase, but I updated the javadoc on it to make that explicit.

I meant provide it an uppercase input, validate output is lowercase.

[mike-burrage-hedera]

There is no uppercase or lowercase input - the input is raw binary bits of the protobuf that