Compute or cache project meta data on program start

[aharwood2]

Project metadata is stored in the DB for speed, so that the calculations are only done when a dependent entity changes rather than every time the value is displayed. However, sometimes, the logic of computation is changed in a patch (e.g. fix for #1318), but the DB values are not updated via a migration because calculation is done in code. One option here would be to add a method call on app start-up that refreshes the computed values in the DB.

• Identify computed values that are stored in the DB
• Call various calculations across the full data on app start up to update the DB values

[aharwood2]

I think the easiest thing to do for now is just to focus on the project meta data which drives the UI summary. I will continue to store these in the DB but I will add an initialisation method so that when the app starts up it recalculates all the stored values and updates the DB using the same method that it would use if it was doing it when you press update on the UI. There are probably other quantities in other tables that are computed but this covers resource costs, subtask costs and project costs which are the main ones we care about I think.