WIP: Add more MNI templates

[ejolly]

This PR adds support for the following additional MNI templates:

• 2009c 1mm and 2mm - used by fmriprep
• 2009a 1mm and 2mm - used my nilearn

Our current default template is the 6th generation 2009 MNI template also used by FSL

• [x] Add MNI template files
• [ ] Add Colin normalized MNI templates to each space
• [ ] Update prefs to support loading new templates