Capabilities

Pull request for the graph.

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The hover tool needs to be controlled here.  It's giving unattractive information.  Either

1.  We should shut if off
2.  We should expose it to a new source of information that I'm happy to supply about that status of each backend/operation pair.

If we're going with (2) (which will require us to understand how hover works) then perhaps we change our data to something that looks like the following:
```Python
+    'SQL':{
+        'Arithmetic': "Generally yes, but math is limited in SQLite",
+        'Reductions':True,
+        'Selections':True,
+        'Grouping': True,
+        'Join':True,
+        'Sort':True,
+        'Distinct':True,
+        'Python Mapping': "Only in Postgres"
```

Any string is considered a positive result.  This text would then go in the hover box, along with the operation and backend names, but without the `(x,y)...` text