Admin features

**Admin resources page:** 
+ Added functional “Expand All” and “Collapse All” buttons to admin resources page.
+ Added functional filtering feature to admin resources page.

**Back-end:**
+ Added new booleans to `FoodResource` model.
+ Added analogous booleans to `AddNewResourceForm`.
+ Added / Refined `serialize` functions for various models.

**Map:**
+ Styled the map using CSS.
+ Updated pin images that are used by map (non-outlined to outlined.) 
+ Added filtering checkboxes to map front-end (not functional yet.) 
Done.