Added hook for per-feature filtering when rendering tracks.
Conflicts:

	src/JBrowse/View/Track/HTMLFeatures.js
Defined standard feature filters for filtering by strand.  Need to generalize soon so tracks can be passed other filters.
Added option to ignore global featureFilter for individual tracks via config.ignoreFeatureFilter.
TODO: might want to generalize this as a featureFilter hook that can specify per-track filter?
convert GenomeView to dojo/declare
convert Browser.js to dojo/declare
make GenomeView a JBrowse/Component, and make its constructor take an args object instead of positional args
wire up support for feature filtering at the level of the browser, the genomeview, and the track
add JBrowse/Util/FeatureFilters, a standard set of feature filters