Rely on the servlet configuration for generating URIs

[arteymix]

URLs are created relative to settings in Gemma.properties, but those are redundant since it is also part of the servlet context configuration. It would also be more robust and work consistently in dev/prod environments.

• [ ] move APIs that generate URLs for Gemma into gemma-web, gemma-core does not need to be aware of the deployment details
• [ ] remove gemma.hosturl and gemma.baseurl and gemma.rootcontext since those are redundant with what the ServletContext provides
• [ ] use ServletUriComponentsBuilder from Spring instead
• [ ] favour relative URIs (i.e. /arrayDesign/{id} instead of https://gemma.msl.ubc.ca/arrayDesign/{id})

[arteymix]

The only place full URLs make sense is when we generate them for external usages like sending an email. I think this is done nicely in the RDP codebase.