Additional tools for working with IBE, including SIA access

PR includes tools for listing the valid / available data sets, missions, tables and a tool for querying the SIA component of IBE (which is the only programmatic way to get image access, as far as I can tell)
Hmmm, there are always three links for each table: columns, docs, and data. The href values seem to be pretty consistent; I don't think a dict is necessary.

Better to list just the table names themselves. We could add a function to grab the list of columns for a given table and another function to navigate the user to the table's docs with [`webbrowser.open`](https://docs.python.org/2/library/webbrowser.html#webbrowser.open).