Be more flexible with scheduling

[eschnett]

Allow adding schedule groups to simplify scheduling of e.g. evolution code and boundary conditions.

Allow specifying where the auto-generated routines (boundary selection and application) are scheduled.

This may be subsumed under the "boundary conditions for non-evolved variables" issue.

[ianhinder]

Now that analysis quantities have boundary conditions applied automatically with automatically generated schedule groups, can this issue be closed?