Add border for tables in documentation

Without border the tables (e.g. in the REST API documentation) are
hard to read.

Change-Id: If750c09c8518bac3575ada606e918bf18ccc57bf
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Documentation/doc.css

@@ -41,3 +41,13 @@ li p {
 dl dt {
   margin-top: 1em;
 }
+
+table.tableblock {
+  border-collapse: collapse;
+}
+
+table.tableblock,
+th.tableblock,
+td.tableblock {
+  border: 1px solid #EEE;
+}