Validate paths used for indexing options for CreateCollection

[tatu-at-datastax]

Currently the only validation done for indexing options of CreateCollections is to make sure that only one of arrays ("allow", "deny") is non-empty.

But we should be able to further validate that all paths included are valid paths for JSON API, same as we do for paths used for shredding and filtering.

For example, currently user could use:

"indexing" : {
   "deny" : [ "_id", "data*" ]
}

expecting data* to be regexp used: it won't and we'd take that to refer to hypothetical value like:

{
   "data*" : 42 
}

but we do NOT allow such properties to be used (character '*' not allowed in path segments).

Adding validation would prevent users from creating Indexing settings that cannot work as intended.