Offline cache support

[sjlouder]

Support saving blob returned from Lastpass server to disk, and populating the vault by parsing the file.

Vault parsing logic will be extracted from Sync-Lastpass folder. Modify Connect-Lastpass to include an -Offline parameter that will skip calling Sync-Lastpass and instead parse the local cache. If the local cache does not exist, Connect-Lastpass will throw an error.

File location: Module directory? Should be a per-user directory

New config: [Bool] Automatically save local cache
default: true

Depends on #60