Add new "User Subscriptions" section

Create a new section in Admin called "User Subscriptions" that will be used for management of subscriptions.

Place new section under User Management section after Mailings section (use default custom icon for now, later we'll have special icon created).

[B]Section visibility:[/B] Visible in Advanced interfaces and Debug ONLY in Simple.

There we are going to have a grid of Subscribers with list of fields that we have in EmailEventSubscribers table.

[B]Grid[/B]

Toolbar: Add, Edit, Delete buttons

[B]Available Columns:[/B]
SubscriptionId
EmailEventId
EmailEventName??? (I think would be good to have)
SubscriberEmail
UserId
UserName or User Email (I think would be good to have)
CategoryId
CategoryName (I think would be good to have)
ItemId
ItemName (I think would be good to have)
ParentItemId
ParentItemName (I think would be good to have)
SubscribedOn

[B]Add/Edit form[/B]
Form should have all necessary fields + friendly selectors where possible.