doc refactoring (#267)

* reformatted docs; moved visualizer section; added references to top; hiding some doctrees etc.

* changed realtime viewer tab

docs/tutorials/data/data_index.rst

@@ -0,0 +1,11 @@
+Data Setup
+----------
+
+# TODO: high level summary
+
+.. toctree::
+    :maxdepth: 1
+
+    choosing_dataset.md
+    creating_dataset.md
+    custom_dataset_format.md