revised system for managing demos; code commenting

Demo files are placed in static/sample_data/demo_genetrees and named
demo_<something>. Currently, it is assumed that these are Newick files
with the "embedded ids" style of names, and that we are going to match
against the Bininda-Emonds mammals tree.

The demo names appear in the Reconciliotastic pull-down menu by virtue
of the following code in reconciliotastic.py, which matches on the
demo_ prefix:

    datalist =
os.listdir(os.curdir+'/applications/shiny/static/sample_data/demo_genetr
ees')
    datalist = [n.split('_',1)[1] for n in datalist if n.split('_')[0]
== 'demo']

The file path is reconstructed later in phylotastic.js with the
following:

	treeFileName = '/sample_data/demo_genetrees/demo_'+treeName;