Check details buttons

Hi,

I've done a bunch of work on the check details screen:

- Grey out submit buttons if they're not available or if they've been used, highlight the file in the file list when you've selected it for preview, etc and show a warning if you're trying to move away without saving.

As well as:

- Show a warning if you've some how come to an already acquitted job. 898ad45
- Certain properties were only available to TIFFs and trying to display them for JPEGs was causing errors. 3c10153
- Move the file preview to the top. f948e53

Huw