all: Stop first-time GOM users from having to set the "new in version"

Applications that use GOM from the get-go shouldn't have to
call "new in version" for every single one for their initial
properties/columns.

Nor should applications with existing columns have to set their
"new in version" to 0 for those columns.

Instead, we'll try to create the table with all the columns
that are new in version 1 in one go, which can fail gracefully.
tests: Add migration test for empty DBs

This is pretty much the same test as test-gom-find, except that
this database is initially empty during migration.
tests: Use a temporary dir for test-gom-find

So that tests don't fail on startup when a failed test happened
beforehand.