Added objective-c client to api docs
Added api resource for retrieving available audio descriptors and docummented it
Removed unneeded 'query' function from similarity client, server and gaia wrapper
Removed unneeded repeated nnSearch calls in search
Basic refactoring to use pca gaia index for basic similarity_search calls
Optimized api_search similarity resource to use pca dataset when possible
Fixes to similarity server to use pca dataset by default