Accounts name loading from `brokers.conf`

[goodboy]

After #205, we actually have all the machinery to load account names from backends with the table-section synax:

[accounts.ib]
ira = 'U3566665'

[accounts.binance]
margin = '3459039485'

We basically just need to add some support to do reverse lookups on brokers who require a particular backend brokerd connection to be established first (eg. ib uses separate api gateway instances to run paper vs. live accounts).

I'm thinking the approach here should be to pass the user specified name to the EMS and have it relay that same name to the brokerd client wherein the actual account # is looked up on the filesystem of the brokerd process. This ensure maximal privacy and avoids the need to encrypt account details (specially) on trusted networks where the user can rely on the brokerd node alone being secured for personal access; this will make group trading architectures likely much simpler as well.

Thots appreciated from the lurkz.