25842 Mari support

- Mari hooks now support loading published geometry into Mari
- Maya hooks add support for loading Mari UDIM textures into Maya 2015
- Added an 'open_publish' method to the app that opens the loader in a modal 'file-open' mode.  This allows an artist to select a publish and then click the 'Open' button which will return the selected publish to the calling code.  This is used by the new Mari New Project command.
- Updated to require core v0.14.66
Please document return value!