Modernize URLs

[arteymix]

Most of these are about adding request mappings and permanent redirections.

URLs in Gemma Web should reflect a better terminology: datasets, platforms, elements, result sets, etc. as we use in Gemma REST.

This makes it easier to navigate as one can simply paste a suitable ID in the address bar.

A few patterns I'm thinking about:

• /datasets/{id}
• /platforms/{id}
• /genes/{id}
• /search

Where identifiers can be any suitable ID.

Previous URLs should be converted into permanent redirections and organized in some kind of legacy controller.

[arteymix]

I've just introduced EntityUrlBuilder in the single-cell branch. I can add a mode for generating legacy URLs.