Improve Linear Focus Algorithm by adding extra outward motion then moving back in.

Summary:
At the start of its first and 2nd passes, the linear focuser moves out to
some position N. Now it will move to N+M and then move back in to N before
starting its inward capture sweep. This is done to remove backlash effects
inside the capture sweep, and to make sure the last motion was inward
to solify the focuser's position. There is also a small fix to a log message
and a bug-fix change to the way maxTravel was implemented in the linear focus
algorithm.

Test Plan:
Main thing to see is that at the start, instead of moving out to a certain
focus position, it moves further out (by 5 focus steps), and then moves back
in (by the same 5 focus steps) before being to capture focus images.

Reviewers: mutlaqja

Reviewed By: mutlaqja

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D26218