Scripted references to body origin planes

Issue imported from https://tracker.freecad.org/view.php?id=3770

* **Reporter:** vectronic
* **Date submitted:** 1/12/2019
* **FreeCAD version:** 0.18
* **Category:** Feature
* **Status:** confirmed
* **Tags:**

# Original report text

As discussed here:

https://forum.freecadweb.org/viewtopic.php?f=22&t=31540

it would be great if the Python API was expanded to provide convenient methods to access the plane and axis of a body origin.

At the moment it is necessary to iterate through the origin features array and match against a label.

I have also written a small summary of the scenario here:

https://vectronic.io/posts/freecad-part-design-indices/

A suggestion would be to support something like:

```origin = App.getDocument('Unnamed').getObject('myBody').Origin
xAxis = origin.xAxis```

# Additional information

OS: macOS 10.14
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.15310 (Git)
Build type: Release
Branch: (HEAD detached at c88a64e8e)
Hash: c88a64e8e7a3bb66a23b965b655b5a5040dfa4d2
Python version: 2.7.15
Qt version: 5.11.2
Coin version: 4.0.0a
OCC version: 7.2.0
Locale: English/UnitedKingdom (en_GB)

# Other bug information

* **Priority:** normal
* **Severity:** feature
* **Category:** Feature
* **Updated:** 2/6/2021

# Discussion from Mantis ticket

### Comment by Kunda1 2019-01-12 13:09
Note vectronic
Please always try to use the most up to date dev version.
Current one is at r15611 you are 301 commits behind it.

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### Comment by Kunda1 2019-01-12 13:12
Since we're in a feature freeze I'm setting the target for the 0.19 cycle.