add method of config builder behaves unexpectedly

[liorella-qm]

the add method of the config builder has a very specific and idiosyncratic behvaior: It only accepts a single item or a list of items. This requires knowledge of internal implementation.

Much better to just let it accept a single item only. This is also the documentation.

[SatyaBade12]

The very first implementation accepted one item, after a discussion with Gal and/or Nikola the support for adding a list of config builder objects was added (effectively we didn't update the doc string).

PS: this issue doesn't belong here, can someone with appropriate rights move this to py-qua-tools?

[liorella-qm]

there are 2 things here:

1. we need to simplify the API. It is aleady quite complicated
2. it only accepts lists, not sequences, and this is already un-pythonic