code: def _account_table(accounts):
          
          accountmap = {}
          for acc in accounts:
              accountmap[acc.address] = acc
              for alias in acc.aliases:
                  accountmap[alias] = acc
          return accountmap
docs: creates a lookup table (emailaddress -> account) for a given list of
          accounts
  
          :param accounts: list of accounts
          :type accounts: list of `alot.account.Account`
          :returns: hashtable
          :rvalue: dict (str -> `alot.account.Account`)