[B+C] Add InventoryMoveItemEvent. Adds BUKKIT-3765

**The Issue:**
Currently there is no event to monitor or cancel hoppers moving items between inventories. 

**Justification for this PR:**
This PR implements an InventoryMoveEvent, that can be used to track automatic movements between inventories. This applies to hoppers but may as well be used for droppers when they have a fully functional Inventory interface.

**PR Breakdown:**
This PR simply creates another event type. Source and destination inventories are available as well as the ItemStack being moved and the Block or Entity (as this can be caused by both, blocks like hoppers but as well entities like hopper minecarts) which induced the transfer. 

**Testing Results and Materials:**
A simple test plugin can be found at https://gist.github.com/TriPhoenix/5207263 It simply catches and displayes the events and cancels all events that try to move dirt.

**Relevant PR(s):**
CB-#### - https://github.com/Bukkit/CraftBukkit/pull/#### - accompanying implementation for hoppers and hopper minecarts (#### will be filled as soon as its available)

**JIRA Ticket:**
BUKKIT-3765 - https://bukkit.atlassian.net/browse/BUKKIT-3765