[#730] Add tracking_raw_table to model

The tracking_raw table was being created by a migration script, but was
not actually defined anywhere in ckan's model. This means that in tests,
ckan.model.rebuild_db() would not clear the tracking_raw table, and the
old data would then leak it into tracking_summary as well. Adding
tracking_raw to the model makes rebuild_db() behave as expected again.
[#730] Make sure 'sort' is always in package_search's data_dict

If data_dict contained no 'sort', the default value was not being added
if the data_dict did contain 'abort_search': True. The code nonetheless
tries to access data_dict['sort'] later on and crashes. (Isn't this what
schemas and validation are supposed to be for?) This was causing a test
to fail. Adding the default 'sort' value to data_dict even if
'abort_search': True is there fixes it.
[#714] Fix some solr package search tests

CKAN used to convert 'sort': 'rank' into 'sort': 'score desc, namae asc'
but since commit ca04063ce061fb80375e73d5aad865ebd6e0ae6d ([#714] Fix
default sort ordering) it no longer does this, which breaks these tests.
Update the tests to pass 'score desc, name asc' directly instead.
[#714] Use score not relevance in default sort order

'relevance' is not actually in the solr schema so it doesn't do
anything, score is the one we want.
[#714] Fix pagination tests

Change create_arbitrary() to always create datasets in the same order,
instead of a different order each time. Update pagination tests to
expect datasets in the new default sort order.