Update 'Load Datasets' docs for 2.0

http://docs.ckan.org/en/latest/loading-data.html

We probably want to change the title of this to _Importing Datasets_ not _Load_.

I think the outdated ckanclient example on this page has already been updated in a pending pull request

Not sure if these sections on loader scripts are still useful, either update them or delete them. If we're going to provide example loader scripts, these should be in the core git repo and have tests.

The write your own loader script bit is incomplete and contains a todo comment

Remove "If you need advice contact the -dev list" that's a generic comment that could apply to any page about ckan so don't say it on random individual pages