First draft of a fix for issue #206

The problem was that the disaggregator used a tuple (1,2) for the
mains for REDD (because the mains is measured by two meters in REDD,
one on each 120 volt split) but it also used 'meter instance=2' for
the first submeter.
Merge pull request #207 from beckel/master

Fixed metadata for ECO data set - thanks!
Slightly updating BuildSys demo to reflect today's code changes in
NILMTK core.
remove ability to manually specify model.

(the removed implementation was ugly as hell (my work!).  Should have
a method for adding manual model.)
Further work on #206.

Today's fixes for #206 have been a little ugly.  The much nicer fix
will be to tackle #195
ignores files that start with '.', which often happens in Mac OS
version update