feature IDs for views (and tables without PK)

[beasteers]

fixes #86

• Adds Database.IDColumn = "id" to config
• Use IDColumn to search table columns for a matching name. Use as a fallback for cases where there's no primary key (views, tables w/o pk)
• Also used to match against function output columns in place of the hard-coded "id" identifier from before

Question: we could make this be Database.IDColumns = ["id"] instead to allow for multiple possible options (first match)