[Fix]: Telephone layout + Telephone deletion

[skyefreeman]

This fixes issue https://github.com/AudioKit/Cookbook/issues/143

Problem

On the telephone Cookbook example:

• digits cannot be fully deleted.
• vertical layout is uneven.

Solution

• Fix delete + phone call digit gating to check for > 0 characters.
• Set a specific vertical spacing value to enforce a uniform layout.

Before	After

[NickCulbertson]

Thanks!

There seems to be some odd behavior when you drag on the call and hang up buttons but that's a separate issue.