Changelog.
Remove some work packages from aggregation.

This removes work packages with either no start or end date from the
rendering of text in aggregations, as well as reducing the amount of
work packages that are considered calculating the space that labels
could occupy in aggregations.
Fixes a bug w/ aggregation text rendering.

Text rendering would be performed for completely obstructed work
packages, which is a bad thing, since there might be many of them.
Limit text drawing in aggregations

Only consider texts in aggregations where there is more horizontal space
than PE_TEXT_AGGREGATED_LABEL_WIDTH_THRESHOLD.
Speed up offset measurements.

When measuring offset values on DOM nodes, store the values back in the
DOM so the measurement does not need to be repeated. For subsequent
measurements on the same element, store the result without ever
accessing the DOM.
removed dead-if