WIP: select language only at project creation

Since the language (or rather, its 2- or 3-letter code) is part of
the project code from which the database (and repository) name is
derived, we should not allow a project's language to be changed
after creation. Instead, we should ask the user to choose a language
during project creation only, and not change it thereafter.
Project codes should be all lowercase
Use project code for database name if possible

Project name should only be used as a fallback if project code (which
is "language-projectname") is not available.
Do not rename project DB when name changes

Since the project DB name is now based on the (immutable) project code,
not the (mutable) project name/title, we should not rename the Mongo
database when the project name is changed.