When using purchaseticket cmd with multiple tickets, use multiple server connections

[raedah]

The current behavior is for a single connection to the server to be used per participant, even if the participant is purchasing multiple tickets. Instead, only add one splittx per connection and open multiple connections if the user is buying multiple tickets.

This is the cmd used to purchase multiple tickets with a single command.
purchaseticket default 50 0 "" 3

[huyntsgs]

This will change current work flow on dcrwallet and dcrtxmatcher server. It may take a while.

[raedah]

It will be challenging to select non conflicting utxos, so this task will be a low priority.