Fix __ne__ error, and add opinionated change to __eq__, in `BasePoseMatrix`

[btalb]

This PR has two parts.

1. Error in != comparisons Comparing two of most things using the != operator currently fails with the following error unless you make them lists:

In [6]: SO3() != SO3()   
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-16fbcbbd9d14> in <module>
----> 1 SO3() != SO3()

~/qut/repos/spatialmath-python/spatialmath/baseposematrix.py in __ne__(left, right)
   1560 
   1561         """
-> 1562         return [not x for x in left == right]
   1563 
   1564     def _op2(

TypeError: 'bool' object is not iterable

This is due to __ne__ assuming comparison results are a list. Commit 13d6ee1 addresses this.

2. An opinionated change to == comparisons Currently a runtime assertion error is thrown if two things are compared of different types.

I know I would find simply receive a False return easier to work with in code, as two different types definitely aren't equal. But that's just one opinion, and I can see how the way it currently is also makes sense.

Happy for this part of the PR to be reverted if desired:

git revert 7297788

[petercorke]

There is precedent for your answer

>>> class C:
...   pass
>>> c=C()
>>> c == 3
False
>>> 

dissimilar objects doesn't raise an exception.