Groups on front page vary in height

The groups on the front page vary in height:

![Screenshot from 2013-03-25 13:23:49](https://f.cloud.github.com/assets/22498/297783/f5453174-9546-11e2-8010-c749e559454c.png)

There are a number of issues:

1. If a group's title doesn't fit on one line, then it wraps and the group block becomes taller than the blocks of other groups with shorter titles (this probably also happens if one group has a longer description than the other)

2. The number of datasets shown per group varies.

3. Do the datasets themselves also vary in height, if they have different length titles and descriptions?

For 2, we could limit the number of datasets shown per group to a fixed maximum, and if the group has more datasets add a "More datasets >" link at the bottom. They would still vary in height if one group had less datasets than the limit.