Add rake task nuke_pave and sample data, modify seeds task

Setups up rake task that setups up the db and sample data with one rake
task. Modifies seed task so that in dev mode many thousands of entries
are not loaded.
"Fix: #7: Update datarefresh task so that new data can be imported from USDA"
Add cron task to refresh data every 20 days
Merge pull request #32 from jwieringa/feature_bootstrap_sample_and_seed_data

Setup sample data for development, update data refresh task, add cron to refresh data