Automatically set new custom nodes as primary

[r-c-k]

Description

When adding a new custom node, firefly should automatically set it as primary.

Motivation

It is likely that a user wants to set the newly added custom node as primary.
Doing so automatically spares a few clicks.

Are you planning to do it yourself in a pull request?

No.

[r-c-k]

Should require #921 to be fixed first