Investigate performance of loading annotations from snapshots

[Nicklas Nordborg]

There are indications (see ​http://baseplugins.thep.lu.se/ticket/398) that the fix for #1685 may have had a negative impact on performance. See also #1374 for information about the initial improvements with the snapshot system.

[Nicklas Nordborg]

I have made some initial tests with an experiment that has 849 bioassays and 9 experimental factors. There is no clear difference for the initial caching (as expected). But after that, the loading times are about 3 times higher with the fix for #1685 in place as without the fix (3 seconds vs 1 second). So there is room for some improvement, even though the absolute loading times are not that bad.

[Nicklas Nordborg]

(In [6065]) References #1693: Investigate performance of loading annotations from snapshots

Added a special case in the permission check that should avoid loading each annotation and item just for the permission check when we are only checking READ permission based on the annotation type. Test results for the above experiment are back to the original values.