Replace Context with ContextWrapper

[cmelchior]

Fixes #3530

This PR replaces our stored Context with a ContextWrapper. This means we use the parsed Context when calling init to retrieve the needed information and then store that.

It has the following benefits:

• Should make Realm works better with Instant Run (Cannot find solid proof of this, but there was a warning in IntelliJ about it)
• Will remove the Android Context from RealmConfiguration/SyncConfiguration/BaseRealm making it easier to support JVM in the future.