T-HtmlCss support for file names to download

[jakubklimek]

T-HtmlCss needs to provide support for the following usecase:

• List of links, get the links and pair them with filenames which I get using another CSS selector
• This may be generalized so that in output RDF, there can be e.g. one subject per table row (list item) with more properties from table columns (link href and text)
• I suggest this is done by supporting "subselects" - one CSS selector selects all table rows and creates a subject and then there will be 2 "local" css selectors to select predicate-value pairs.

[skodapetr]

We can use options like: (name, query, isFinal, subject, output) name - named of the query also if data are stored under this name, then this named-query is applied query - css selector isFinal - if true then triple is created from resulted value, as a predicate the value in "output" is used, as a subject last "valid" subject is used subject - if set then a subject is created for this entity, if a following named-query is final it will use this object, unless other named-query does not redefine subject. For the purpose of statement creation the given statement will be suffixed with a number to make sure that created subject is unique. output - named of output ie. data name or predicate based on isFinal flag