Added dump/load to IndexTool

IndexTool now supports dumping data out of tables into JSON, and loading
it to other tables from a file.

Implementation works but isn't well tested. Mostly to support working on
a test database for index_server development.
Move metadata validation to Utils

Moved the validation method from FusionIndex to Utils. This allows one
to validate the metadata without having to actually call the
index/update methods. The method also provides a string response with a
complete list of what's wrong with a given metadata map, which is
probably more generall useful than before when it barfed up an
InvalidArgumentException on the first problem.

This is mostly to support the index_server, since it'd be nice to
provide better information about what's wrong with the data (preventing
round trips).