Convert star * import to regular import

[angelofallars]

main.py imports tkinter and time using * imports. This will pose an issue once we add more and more features (and thus modules) to Pomodrip. If a function from Tkinter and another function from a module have the same name, they will clash and cause errors. Changing to regular imports will improve the readability of code as well.

Suggested actions

• Change from tkinter import * to import tkinter as tk
• Change from timer import * to just import timer
• Update the functions that use tkinter to reflect the changes above like StringVar() to tk.StringVar()

[ryanamay]

Also cross-reference to this: https://www.python.org/dev/peps/pep-0008/#imports