Add offline object saving

[vdkdamian]

New Feature / Enhancement Checklist

• I am not disclosing a vulnerability.
• I have searched through existing issues.

Current Limitation

It's not possible to use Parse-Swift offline.

Feature / Enhancement Description

It would add offline object saving, related to the requested query.

Example Use Case

var query = GameScore.query("points" > 50)
    .useLocalStore()
    .order([.descending("points")])

Alternatives / Workarounds

None

3rd Party References