Enable vendoring using GOVENDOR

Benchmarking

Resolves - https://discuss.dgraph.io/t/vendoring-dependencies-for-dgraph/177

Pertaining to the discussion mentioned above: GLOCKFILE has been removed,
README has been updated, and vendor/vendor.json has been added. At this
point of time we are only adding dependency information file(vendor.json) and
not the actual dependencies. This commit also helps avoiding
installation of dependencies in $GOPATH if vendor directory is synced
using govendor.

1. Changing extension of files with binary data to .bin.
2. Running separate benchmark for each query according to numElements in their
result.

1. Exporting query and result byte slices inside SubGraph so that they are
written to file when we write the SubGraph to file after gobencoding it.
2. Added benchmark test to benchmark ToJSON and ToProtocolBuffer methods for
actors and directors query for 10,100 and 1000 entities in the result.

Output the offending line in error log if rdf.Parse fails.

Grpcerror

Functionality to find first N results

Added helper functions for Graph response to client

preTraverse()

Removed the unnecessary extract function and result struct. Now preTraverse
directly acceses flatbuffers to get values and uidmatrix.
Renamed struct fields in the protocol buffer schema file.