Select multiple categories of material

[stephanie-fu]

Long-press (like Android photo select) to select multiple categories of recycling bins.

[stephanie-fu]

Idea for this enhancement:
Move the onClickListener for the material buttons to a new method in the new Maps class I created.
Call the method if one button is short-tapped, or if one is long-tapped and ok is pressed after selecting multiple materials.
Add the materials selected to an array, and add the coordinates to each material in the array onto firebase.