GSOC - media package for the platform

##### Media package manual
https://github.com/kaviththiranga/joomla-platform/blob/media_package/docs/manual/en-US/chapters/packages/media.md

##### Previous discussion thread

https://groups.google.com/forum/?fromgroups=#!topic/joomla-dev-platform/gsozoo4B2Jw

In the previous discussion, some modification were suggested such as removing the usage of JFile, refactoring JMediaCombiner as JMediaCollection etc.

I am creating this pull request, after committing those modifications.

##### Media package

https://github.com/kaviththiranga/joomla-platform/tree/media_package/libraries/joomla/media

##### Tests for media package

https://github.com/kaviththiranga/joomla-platform/tree/media_package/tests/suites/unit/joomla/media