* [#397] Checkpoint format that supports NU5 TreeStates
Closes#397
This commit adds `orchardTree` value to WalletBirthday and renames
the value `tree` to `saplingTree`. It also modifies the checkpoint
JSON files accordingly. It adds `.testnet` and `.mainnet` checkpoints
for orchard activation height.
* rename `sapling-checkpoints` to `checkpoints`
Francisco Gindre