Show last x days of builds from newest build instead of from today

[cburgmer]

Working with outdated sync can be tedious and unintuitive as the build data slowly vanishes from the graphs, as newer dates are just empty if no new sync has been undertaken. In the case of the examples inside the repo, they just plainly don't show anything for historical builds, if they are e.g. a year back.

Rather let's just show the last x days/months offset from the latest build synched.