Add validation rules to account creation

[aaroncox]

Currently there are no rules while creating an account, and when creating an account with an invalid name, it looks like it creates them (but nothing happens on-chain).

[eastmaels]

Yes, this is confirmed. I tried creating one today and it didn't give me an error when the length of the account name exceeds a certain number of characters.

The account name I tried to create was eastmael.autovote. When I tried to create it via steemconnect, I was only allowed to type eastmael.autovot (no e at the end).