Adds a page to the admint panel which allows an admin to upload a custom emoji by uploading a name, shortcode, description, and image. These fields are editable whenever the user re-vists the page. The emoji data is loaded from, and saved into SiteConfiguration, while the image data is loaded from and saved to DefaultStorage.

Further work that needs to be done:
* Enforcing mandatory fields that user must fill out before clicking "Save", so as to not raise an error.
* Adding labels to the form fields, and removing the extra "name" field at the very top of the form. 
* Rendering a preview of the emoji when loading the page (through get_context() in EmojiFileUpload).