snippets: remove alternate shortcut feature

nobody needs alternate shortcuts for text snippets and it makes the UI
much cleaner
CCMAIL:dhaumann@kde.org
session-persistent tabs in Kate

With this patch, the view space restores its LRU document list, so that
all tabs of a previous session reappear (as many as fit). Consequently,
if you only use one viewspace, you always have as much tabs visible as
possible. This is a good behavior, since otherwise users might be
confused why all the opened documents disappeard from the tabbar.

REVIEW: 120434
use KPluralHandlingSpinBox where apropriate

Thanks to Dominik Hauman

BUG: 336332
Add KBProcess to get "shell command" previously provided by KProcess