Provide top-level summary of dataset access points

[LucaCinquini]

The web portal UI would benefit from knowing wether a dataset is exposed via HTTP, GridFTP, OpenDAP etc in order to properly display the hyperlinks. For example, such information could be used to selectively display Globus Online links.

Additionally, the search back end could allow querying of datasets that are exposed via LAS, via OpenDAP, and so on.

[LucaCinquini]

The requested information is now stored within the top-level dataset metadata as a multi-valued field called "access", which may be returned as part of the record metadata. For example access="LAS", "HTTPServer", "OPENDAP".
The field values are the THREDDS allowed valued for the "serviceType" field.

Additionally, the search back end allows querying of datasets by "access" parameter, for example:
http://esg-datanode.jpl.nasa.gov/esg-search/search?distrib=false&access=OPENDAP