IDLE: replace DynOptionMenu with a ttk Combobox or OptionMenu

GitHub fields:

assignee = 'https://github.com/terryjreedy'
closed_at = None
created_at = <Date 2016-08-13.19:52:27.674>
labels = ['expert-IDLE', 'type-feature', '3.7']
title = 'Retire DynOptionMenu with a ttk Combobox'
updated_at = <Date 2018-06-27.22:03:03.630>
user = 'https://bugs.python.org/jfoo'

bugs.python.org fields:

activity = <Date 2018-06-27.22:03:03.630>
actor = 'markroseman'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2016-08-13.19:52:27.674>
creator = 'jfoo'
dependencies = []
files = ['44097', '47652']
hgrepos = []
issue_num = 27755
keywords = ['patch']
message_count = 17.0
messages = ['272609', '272673', '272699', '272757', '272974', '279041', '279043', '279175', '279176', '298091', '298381', '299816', '299820', '299861', '299867', '320459', '320466']
nosy_count = 4.0
nosy_names = ['terry.reedy', 'markroseman', 'jfoo', 'cheryl.sabella']
pr_nums = ['3215', '7979']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue27755'
versions = ['Python 3.6', 'Python 3.7']