refactor: identity root account and network root account

[hanwencheng]

Extract Identity root account and network root account from the clickable heading.

UI display

Now Identity root account is in the custom network account list, and network root account is in the correspond network account list.

identity root account	network root account	network chooser list

Account Generation

• The network root account will be automatically generated when user choose to add the certain substrate network.
• The identity root account will be generated when user explicitly derive a custom path with empty string.

identity root account	network root account