update CKAN in ODN to 2.3.5 (plan was 2.5.2)

[hanecak]

We have CKAN 2.3.2 in ODN 1.2.4 1.3.0 .

As of now (17.3.2016) following new releases of CKAN are available (see http://docs.ckan.org/en/latest/changelog.html):

1. 2.5.2
2. 2.4.3
3. 2.3.4

We need to keep up with upstream and update to CKAN in ODN to 2.5.1 2.5.2 or some lower but newer version to bring bugfixes and new features to ODN users.

[hanecak]

CKAN API changed quite dramatically in 2.4.0+ (compared to 2.3.2). This has impact for other modules (ckanext-odn-ic2pc-sync, ckanext-audited-datastore-api, UVPlugin-relationalFromCKAN, UVPlugin-filesFromCKAN, UVPlugin-filesToCKAN, UVPlugin-relationalToCKAN, UVPlugin-relationalDiffToCKAN) and Martin's estimate of amount of work required is higher then expected.

Thus this will most probably not make it into 1.3.0 .