Feature/gene tree stats

Hello,

The stats for gene-trees used to be .inc files, generated by our release coordinator and included in the html pages. Now, the pipeline is able to generate the statistics and store them in the database. The following changes (together with the pull-request on public-plugins) bring in dynamic views for gene-tree stats
I've based my changes on what Anne wrote for the whole-genome alignments (EnsEMBL::Web::Document::HTML::Compara::GeneTrees)

I've had to change one thing in the raphael javascript file for the piecharts: it used to group all the categories that were minor into a new category "others". I've checked with Laurent with Variation, and the change will not affect them.

Before / after:
http://www.ensembl.org/info/genome/compara/prot_tree_stats.html
http://www.ensembl.org/info/genome/compara/nc_tree_stats.html
http://enssand-02.internal.sanger.ac.uk:9073/info/genome/compara/prot_tree_stats.html
http://enssand-02.internal.sanger.ac.uk:9073/info/genome/compara/nc_tree_stats.html

Matthieu