Add energy cost to AbilityData

Currently there seems to be no way to find out how much energy using an ability costs

Cost itself is already mentioned [in a comment in data.proto](https://github.com/Blizzard/s2client-proto/blob/blizzard_internal/s2clientprotocol/data.proto#L11). I suppose this means energy cost, because for building units and researching upgrades the cost data is already available, and for others there is no mineral or vespene cost:

```proto
// Stuff that may be important: cost, range, Alignment, targetfilters.
```

Start by reading data.proto, especially the AbilityData definition and the comment identifying cost as important. Compare the requested energy cost with the cost data already represented for units and upgrades. Done means AbilityData exposes an energy cost that can be obtained through the protocol.

Written by the indexing model from the issue text.