This closes #84

   1- [iOS] Only perform 'seek' operation if both avPlayer and avPlayerItem are ready,
        send error to client code if they aren't ready.
   2- Deplay Media File Playing by a few seconds so that 'seek' operation happens only
        after enough buffering has been done.

CB-10476 - fix problem where callbacks were not invoked on android due to messageChannel being overridden by callbackContext in every execut() call. This closes #78

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X-ref: https://github.com/apache/cordova-plugin-device/pull/48

This will still intermittently fail test 19 but this is more to do with
the success criteria of that rest.  rate is applied and works.

This reverts commit e7f9f048.

Fixed example referencing non-existent variable media, fixed to use my_media variable.

#62 addresses the following : Closes #18, Closes #12.

add support for streaming url prefixes that do not end in a file
extension
add base requirements for enabling background audio in a windows app

# Conflicts:
#	plugin.xml
simple conflict on version with my branches previous version bump.
Resolved to match master.

seekto 0 then stop playing.