Improve IATI Export

[KasperBrandt]

The IATI export is currently too slow, and gives a timeout.

Test plan

GIVEN the My IATI section in MyRSR
WHEN an organisation is selected
THEN all projects of which that organisation is a reporting organisation should be listed
AND the page should not timeout for organisations with more than 100 projects

GIVEN the projects are listed
WHEN the 'Perform checks' button is clicked
THEN the button should disappear
AND the projects should one by one turn green or red

GIVEN the checks have been performed
WHEN only green projects are checked
AND the 'Create IATI file' button is clicked
THEN the IATI file should be generated

GIVEN the IATI file is generated
WHEN the IATI file is validated on http://validator.iatistandard.org/
THEN all checks should be passed