Allow user to specify an "environment" rather than CLE/not CLE.

This is the basic version of allowing a user to create an Analysis Project that runs as themselves.  Logic based on the "is_cle" flag is removed (and the flag is preserved only for LIMS compatibility).  The environment of the "run_as" user controls the execution (such as queue selection and disk groups), so properly setting run_as is sufficient to select the correct environment for now.

Perhaps control of the environment may eventually fall directly to Analysis Projects; if we do make real environment types they are uniquely implied by the run_as user so we aren't missing anything by not storing them for now.

[This supersedes #189.]