introduce a first version of options for configuration blocks

The basic idea/goal of configuration blocks is that the configuration
system can read a configuration text file and then configure the
blocks accordingly.  This is made a lot simpler if the configurable
options on the blocks can be set via a uniform interface.

This is just a first draft of such a mechanism that allows to add the
options and set them by name from the python side.  All I want from
this MR is a basic interface that allows to add the options on the
individual blocks and set them through a python interface.  That will
then allow me to update all the configuration blocks to expose options
before I move on.

The mechanism for setting option values is even more rudimentary,
doing just the minimal thing to allow setting the properties through a
standard interface.  This is mostly there to allow me to move forward
somehow, but some details may change.  The interface I have right now
is probably not ideal for anybody, neither for the text nor the python
configuration.  That probably needs some changing at some point.

There is a much more sophisticated prototype available, but because of
its complexity I didn't want to incorporate it into this first draft.
Instead the interface I have should be (mostly) compatible with the
interface that prototype exposes.  It can then be retrofitted in here
at some point.  The full prototype is here:
https://gitlab.cern.ch/jburr/configblock/-/tree/master/

Also: For photons the recomputeIsEM option should probably not be
repeated in both the calibration and selection blocks.  There needs to
be a special method for forwarding options from one block to the next
which will come in a future update, or when the full option mechanism
gets incorporated here.