Sorting. Tests remain broken. We fixed some.

algo/uidlist.go

algo/uidlist_test.go

cmd/dgraph/.gitignore

cmd/dgraph/main_test.go

cmd/dgraphloader/main_test.go

geo/s2index.go

geo/s2index_test.go

posting/index.go

posting/index_test.go

posting/lists.go

query/geo_test.go

query/query.go

query/query_test.go

schema/schema.go

task.fbs

task/Sort.go

task/SortResult.go

types/index.go

types/sort.go

types/sort_test.go