Add "loading" & "no-internet" indicators to the menus

[HirdayGupta]

Motivation
Right now, while the menus are loading, the user only sees a blank menus. And if the user doesn't have an internet connection, the API just fails silently and menus are blank again. (Simulate these situations and check it out).

The Task

1. Figure out where in the lifecycle for the MenuVC these changes would be necessary. (this is a huge step and involves a lot)
2. Figure out how to check when there's no internet connection.
3. For now, add placeholder labels (saying "no internet" and "loading..") in the storyboard and initialize them as hidden, and then unhide them under the requisite conditions.
4. These labels will be replaced by graphics that will be coming soon from our designer. Issue will be updated to reflect these, but the pending graphics shouldn't hinder the groundwork necessary for this issue.

Acceptable Criteria

• When menus are loading (that is, while menu API is still waiting to for the response) - the "loading" graphic/label should appear.
• If there is no internet connection, an "No internet" label / graphic should appear.

[HirdayGupta]

Those are the images we'd like to use for the loading animation - the image being displayed will change with a timer. We can discuss implementation details about this later, but start with just the label described above!

Thats the scale - the size we want to display the image at: