Batch Annotate with Read-only (rebased onto dev_5_0)

This is the same as gh-3127 but rebased onto dev_5_0.

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NB: This is critical for @imunro to allow public (read-only) data to be downloaded.

This removes the blocking of batch-annotate panel when any items that can't be annotated are selected.

It allows E.g. download of files and inspection of current annotations / paths etc. without allowing annotation.

To test:
 - Select multiple P/D/I belonging to another user in a Read-only group.
 - Batch annotate panel should show.
 - You shouldn't be able to add annotations, but can see existing ones.
 - Can download original file, inspect path on server etc.
 - Banner warns that you can't annotate. Is this too aggressive?

![screen shot 2014-10-21 at 16 25 22](https://cloud.githubusercontent.com/assets/900055/4721194/036a8a50-5937-11e4-840c-4e4dd6fead24.png)