API change: flat cell arrays instead two-dimensional

[martinthenext]

Concepts from our API mirror the corresponding concepts from Office Interop Excel API.

Here we iterate over a range in two loops. We need to:

1. Check if one can iterate over the Range in one loop.
2. If this is the case, change our API so that Action and Event objects have cells attached to them as a flat array instead of a two-dimensional one.