New demo program to enable you to quickly test out the different look and feel settings

DemoPrograms/Demo_Change_Look_And_Feel_Browser.py

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+import PySimpleGUI as sg
+
+"""
+    Allows you to "browse" through the look and feel settings.  Click on one and you'll see a 
+    Popup window using the color scheme you chose.  It's a simply little program that demonstrates
+    how snappy a GUI can feel if you enable an element's events rather than waiting on a button click.
+    In this program, as soon as a listbox entry is clicked, the read returns.
+"""
+
+sg.ChangeLookAndFeel('GreenTan')
+
+layout = [  [sg.Text('Look and Feel Browser')],
+            [sg.Text('Click a look and feel color to see demo window')],
+            [sg.Listbox(values=sg.list_of_look_and_feel_values(), size=(20,12), key='-LIST-', enable_events=True)],
+            [sg.Button('Show Window'), sg.Button('Exit')]  ]
+
+window = sg.Window('Look and Feel Browser', layout)
+
+while True:             # Event Loop
+    event, values = window.read()
+    if event in (None, 'Exit'):
+        break
+    sg.change_look_and_feel(values['-LIST-'][0])
+    sg.popup_get_text('This is {}'.format(values['-LIST-'][0]))
+window.close()