Make stricter writing, align Addresses fields to the library style

[vanous]

• Update the library to be a bit more strict when writing
• The Addresses.address and Addresses.network should be plural (list) like in all other places. I think that there is a small usage, so i will introduce this breaking change.
• add better aliases to serialize scene and user_data:
  mvr_writer.serialize_scene(mvr_read.scene)
mvr_writer.serialize_user_data(mvr_read.user_data)

[vanous]

@nrgsille76 this PR is a breaking change, it is a very small modification but one that bothered me for a while, because it is different then the rest of the library approach. Rather then keeping a bunch of machinery around for compatibility forever, i decided to just change it, please update on your side. Previous (pseudo code):

fixture.addresses.address
fixture.addresses.address.address1
fixture.addresses.address.address2
fixture.addresses.network.network1
fixture.addresses.network.network2

is now
fixture.addresses.addresses
fixture.addresses.addresses.address1
fixture.addresses.addresses.address2
fixture.addresses.networks.network1
fixture.addresses.networks.network2

See the open-stage/blender-dmx#322 , the update was simple:

- for address in fixture.addresses.address:
+ for address in fixture.addresses.addresses:

...

- addresses=pymvr.Addresses(address=new_addresses),
+ addresses=pymvr.Addresses(addresses=new_addresses),

I have also added a nicer convenience serialize methods for scene and user_data, but the originals are still present:

mvr_read.scene.to_xml(parent=mvr_writer.xml_root)
mvr_read.user_data.to_xml(parent=mvr_writer.xml_root)

mvr_writer.serialize_scene(mvr_read.scene)
mvr_writer.serialize_user_data(mvr_read.user_data)

The pymvr with this change has been pushed to pypi, i am planning to push BlenderDMX probably this weekend.