Profile for assembling the Desktop Web UI

* the assembly now imports the webui instead of the other way around
* reorganized the assembly descriptors a bit to avoid duplicating the contents three times.
* everything from the braille profile in the pom is duplicated in the webui profile - I don't know how to avoid that
* the server version of the webui is still only available from the webui repo. we could add it to the assembly but it would just be a simple copy operation (unless we want to include the README or something...)
* ~~TODO: I've copied over the NSIS stuff from the webui repo to the assembly repo but haven't tried to get it working yet.~~