Dev PR/issue fix: Proposal for a patch to the UnencryptedKeystore

A fix for the Keystore as specified
here: KeyFilePath varies from default installation path of keys · Issue #545 · near/near-api-js · GitHub.

In summary the keystore for reading keys from disk has outdated directory format assumptions. The proposal here is to fix this. In the issue there are several courses of action to take. Would be awesome to get some feedback on the patch suggestion.