Make Epic Initial Estimate calculate from features

Before we have solid detailed estimates we like to add initial estimates to get a very general ballpark of feature sizes. However, these initial estimates cannot be applied to the epic estimate. We need to consider these stories' point values in estimation.

Improve capacity tracking by providing an initial estimate of epics based on their features.

Similar to how Detailed Estimate on an epic can be calculated from sums of detailed estimates of features, allow calculation of initial estimate from the sum of initial feature estimates.