Missing/isolated taxa messages (phase 1)

This includes the static/generic messages for missing and isolated taxa in the synthetic-tree viewer. See screenshots below for examples. Note that I've removed the awkward phrase "not a proper clade" and switched the messages (most likely explanations) shown for the missing vs. isolated taxon.

![screen shot 2014-08-19 at 5 26 51 pm](https://cloud.githubusercontent.com/assets/446375/3973451/f6dfba06-27e7-11e4-9380-6a7de63fd33e.png)

![screen shot 2014-08-19 at 5 27 07 pm](https://cloud.githubusercontent.com/assets/446375/3973456/fcdd81a4-27e7-11e4-9b66-f52bb45c7188.png)