Cache scores and improvement status into an Account model

[deborabonner]

-- Numbering: Page 2 should continue numbering from page 1, rather than start from "1".
-- No re-ordering: Pivot Interiors, Inc. - after they completed the Assessment and Planning, they went from being 9 on page 1, to 14 on page 2.
-- Sorting: Activate functionality of the sort arrows next to the column headings. They are not currently functioning.

[smirolo]

These are symptoms of computing the data necessary for the "reporting entity" page on-the-fly instead of picking it from a table in the database. All filter/sort functions are only available on QuerySet (i.e. django-extra-views).

[smirolo]

We might have to do this in order to improve performance of sort (#176) and search (#177)