rename Browser.js makeShareURL method to makeCurrentViewURL
factor wiggle track scaling out into a separate JBrowse/View/Track/Wiggle/_Scale class
calculate per-horizontal-pixel scores and store them in the block before rendering graphics
refactoring Wiggle tracks in prep for implementing region stats
if region or global data stats have same min and max, set one of them to zero for better displayability
implement getRegionStats in JBrowse/Store/SeqFeature base class based on feature scores, in a way that should work for any quantitative data backendj
bugfix to global wiggle autoscale setting
make WiggleBase track default to global autoscale
factor FeatureCoverage track coverage calculations into JBrowse/Store/SeqFeature/Coverage, which is a store that encapsulates another store and calculates its coverage.  also make FeatureCoverage tracks default to local autoscaling.
factor CoverageFeature out into a separate module
fix getGlobalStats in Store/SeqFeature/Coverage
disable dijit highlighting in track pane dndsource
make GenomeView report the visible region in round coordinates only
refactor MismatchesMixin into JBrowse/Store/SeqFeature/_MismatchesMixin  and   JBrowse/View/Track/_AlignmentsMixin.  make the SNPCoverage track work with local autoscaling, and have it use it by default
add featureCount and featureDensity to default region stats calculation
fix selenium tests for sequence track default name changes
merge dynamic_scale branch, closes #203