Updates to saved state directory structure

Per Leemon's request, we should make the following changes to the directory structure for saved states.

The current format is as follows:

```
data/saved/com.swirlds.foobar/1234/mySwirld/1000
|--------| |----------------| |--| |------| |--|
| | | | |
| mainClassName | | round
| | swirldName
location where selfId
states are saved
```

- instead of `selfId`, we should call it `nodeId` (documentation change)
- Instead of `swirldName`, we should call it the `ledgerId`. (documentation change)
- the ledger ID should be a hex value, and for mainnet it should be `00`.
- we should add another directory layer for shard. Each shard should have its own directory. This directory should come immediately before the round.
- swap the order of `selfId` and `ledgerId` (the `ledgerId` should come first)
- names for each directory should be self documenting

Proposed format:

```
data/saved/com.swirlds.foobar/ledger-00/node-20/shard-2/round-42
|--------| |----------------| |-------| |-----| |-----| |------|
| | | | | |
| mainClassName | | shard |
| | node Id |
location where ledger ID round number
states are saved
```