Create a mechanism to display the available objects when in interactive Python mode

Nobody has claimed this yet.

Allowing the user to display the list of available PyDV objects will make it easier to create custom "PyDV Macros" like below (courtesy of Rob Managan):
```
[PyDV]: cur a.4 b.4
[PyDV]: drop
Starting Python Console...
Ctrl-D to return to PyDV
Python 2.7.10 (default, May 26 2015, 14:17:46)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-11)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> def testFunc(line):
... print " this is a test, here is rest of line '", line, "'"
...
>>> self.do_test = testFunc
>>>
Python Data Visualizer 2.3 - 11.20.2017
Type "help" for more information.
[PyDV]: test hhh rest of input line jjj
this is a test, here is rest of line ' hhh rest of input line jjj '
[PyDV]:
```

The issue names no files or tests; start by locating the interactive Python mode and how PyDV objects are exposed there. Use the example macro as the behavioral reference, and consider the work done when users can display the available PyDV objects while in that mode.

Written by the indexing model from the issue text.