don't use model->bounds() here: it's costly!

little control window" problem... without using a monolithic "single
window" design like ParaView & co

- added very basic model selector

- separate setNode and tagNode in API

  integer tags per step data
- ported Eigenvectors and StreamLines plugins to the new post-pro API

add a Universal Transverse Merctor field, add latitude / longitude and UTM coordinates in Plugin/GSHHS.cpp

ported Warp, SphericalRaise and Eigenvalues plugins to the new post-pro API

- ported Gradient, Curl, Divergence, Integrate and Transform plugins
  to the new abstract post-pro API

- documented new post format