ACTION-87 Issues regarding keys in Initialization Data have been added/modified

Per our recent F2F discussion - I have added or updated several issues that impact the support for keys in Initialization Data.

These are the issues in question:
* https://github.com/w3c/encrypted-media/issues/41 <https://github.com/w3c/encrypted-media/issues/41> - Update algorithms to reflect keys being provided in the Initialization Data <https://github.com/w3c/encrypted-media/issues/41>
* https://github.com/w3c/encrypted-media/issues/52 <https://github.com/w3c/encrypted-media/issues/52> - Remove reference to keys in Initialization Data definition <https://github.com/w3c/encrypted-media/issues/52>
* https://github.com/w3c/encrypted-media/issues/53 <https://github.com/w3c/encrypted-media/issues/53> - Allow for long-lived key encryption keys (aka "master" keys) to increase performance <https://github.com/w3c/encrypted-media/issues/53>

Please take a few minutes to review each one and provide feedback if you have any. Note that Issue 41 was renamed and modified a bit, but most of the text is the same.

Joe