Uri to URI

[jotelha]

We use the acronym URI all capitalized in Error names and documentation, let's make it consistent.

• Standardized spelling of Uri to URI in models and schemas for all occurrences.
• There have been two overlapping definitions of BaseUriSchema in sql_models.py and schemas.py. Do we need two distinct definitons? Threw out one of them.
• There have been issues with inconsistent capitalization and overlap of class names when auto-generating client API from the REST documentation (more detail https://github.com/jic-dtool/dtool-lookup-server/pull/27).