local op majority
Refactor local op method minority
Refactor local op method Variety.
Add Majority methods.
Add minority methods.
Fix variety doc.
Add tests for Variety.
Add mean method.
Merge branch 'master' into localops

Conflicts:
	core/src/main/scala/geotrellis/raster/op/local/LocalOpMethods.scala
Merge pull request #770 from sconealone/localops

Localops