[#1792] Add "datapusher submit" paster command to migrate data

I've changed how we create the datastore resources in this issue, both adding
indexes and changing how the "_full_text" column is created. This means that we
have to migrate existing data when this is merged.

The best way I found to do so was creating a new "paster datapusher submit"
command, which reloads every resource in the datastore, ignoring if the file
haven't changed. This is equivalent to deleting every datastore table and
reloading the resource.

The disadvantage of this is that it'll only work if the source data is still
available, and it'll remove any data that isn't on the source data (that was,
for example, added through the API).