Change default shortcut for "Zoom To Fit" action

Summary:
D14201 sets Ctrl+0 as system default shortcut for
Actual Size (KStandardAction::ActualSize). Ctrl+0 is
used by Cirkuit as shortcut for Zoom To Fit.
To avoid conflicts if D14201 is landed this patch changes Cirkuit's
default shortcut for Zoom To Fit to Ctrl+1.

Test Plan:

1. Open Cirkuit
2. Check if no shortcut conflict warnings appear
3. Load a file and check if zoom shortcuts work

Reviewers: kmorwinski, asturmlechner, rkflx

Reviewed By: rkflx

Subscribers: rkflx

Differential Revision: https://phabricator.kde.org/D14202