Increased Facebook Functionality

## Changes/Features of this pull request include:

* Facebook Login button added on bottom of screen (Needs to be incorporated into design better)
* When adding a plant, the add is rejected if the user is not logged in to Facebook
* After adding a plant, the user's name is uploaded to the database (Updated model)
* When viewing plants, a Submitted by field is added which shows the user whom added the plant. 

Next steps:
* The Submitted By field needs to be removed from the Add-plant modal. Yet kept on the modal when viewing plants.
* Camera-functionality