CHANGE: vaultHandler to networkHandler

Desired terminology is to use "vault" to describe the on-chain addresses that contain external funds (asgard or yggdrasil).

However vault is also currently being used to contain internal network logic, such as block rewards, emissions, reserve and more.

#690 (closed) will change /vault_data to /network so should rename the current vaultHandler to networkHandler which should only contain logic for block rewards, bond units, emissions etc.

https://gitlab.com/thorchain/thornode/-/blob/master/x/thorchain/manager_vault_v1.go