G2 should wrap term expansion and definitions in P elements

In the current 1.16 version, both of these, as well as the term time period, are themed as simple boxes, which prevent easy themeing because this is a very generic container used throughout Drupal.

These boxes are the ones introducing the DIVs.

It is not possible to change the DIV used to wrap definitions for a P because most definitions will typically contain several P elements themselves, and P elements can't be nested, by the (X)HTML DTD.

G2.module version 1.17 introduces a more generic workaround: 3 new themeable functions have been added, for expansion (header), definition (body) and time period.

By default, they use theme_box, but can be overriden by themes.

The same version also removes some unneeded DIV wrapping in blocks.