Re-save installation is allowed if LDS is enabled

[hermanliang]

Following PR #579
The installation data will attempt to resave if installation is removed on the server.
But the resaving is not allowed when the local datastore is enabled due to objectID is unchangeable in offline store.
But I think in this case should be allowed .

1. The setObjectId(id) seems only updating the in-memory map (call sequences: 1 -> 2 -> 3). Maybe just unregister old object from the map when setObjectId(null) and allowing ParseInstalltion type only.
2. The ParseInstallation offline store (database) will be updated after resaving (call sequences: 1 -> 2 -> 3). The code seems okay does not need to be changed.

Plz correct me if I'm wrong. 😄

[rogerhu]

Sounds ok but is it possible to make this consistent on iOS?

[hermanliang]

I think it is possible. I'll submit a PR to make this consistent on iOS. 😄