Incorrect default encoding (ISO-8859-1) assumed when submitting SPARQL query as POST request

[SimonBin]

According to the SPARQL standard https://www.w3.org/TR/sparql11-protocol/#query-via-post-direct

the encoding of the data must be UTF-8

Blazegraph uses the getReader method:

database/bigdata-core/bigdata-sails/src/java/com/bigdata/rdf/sail/webapp/QueryServlet.java

Lines 919 to 922 in bc439f9

	if (RESTServlet.hasMimeType(req, MIME_SPARQL_QUERY)) {
	// return the body of the POST, see trac 711
	return readFully(req.getReader());
	}

which defaults to ISO-8859-1:

https://github.com/apache/tomcat/blob/7c0dd42ac4e9533d73d4ba50791ab2dda9d79760/java/org/apache/coyote/Constants.java#L30

This causes charset to break with the following query:

curl -H "Content-Type: application/sparql-query" -d "SELECT ?x { BIND('Curaçao' As ?x) }" https://query.wikidata.org/sparql

For example, this problem occurs when Jena wants to query Wikidata from a SPARQL SERVICE clause, see apache/jena#1259 (comment)

It is most likely also causing Issue #206