Adds new model-type Harvest
Updates the show_service view to use harvest

We want to show a service's status based on it's last harvest attempt.
Updates services views for harvesting support
Adds timeout handling for SOS endpoints
Removes SFMC from Gliders Page
Replaces glider plan thumbnail
Makes links clickable on /gliders

Fixes #230
Adds total datasets and services to overlay

- Landing page overlay
- New method in Datasets to find total that's consistent with dashboard
Merge pull request #245 from lukecampbell/harvesting

Refactor Harvesting framework
Merge pull request #246 from lukecampbell/233

Removes SFMC from Gliders Page
Merge pull request #247 from lukecampbell/231

Replaces glider plan thumbnail
Merge pull request #248 from lukecampbell/230

Makes clickable on /gliders
Merge pull request #249 from lukecampbell/225

Removes start and end times from metadata forms
Merge pull request #250 from lukecampbell/224

Adds total datasets and services to overlay
Fixes metadata table sizing
Better margins
Renames Metadata -> Asset Inventory