This fixes a crash on RHEL7 at the cell function because
the first column of the result fit workspace did not contain
workspace names, but log values instead. This caused issues
when casting the data to a string for comparison. This adds
a check to make sure the column is SourceName before trying
to find the appropriate workspace.

Fix plotting integrated peaks in sliceviewer with no background

Squash python implicit cast warning (ornlnext)

Fix ellipsoid background shape plotting

When plotting the background shell if slice point doesn't go through peak center the thickness calculation was wrong.

python38 gives the following warning when starting up mantidworkbench
```python
DeprecationWarning: an integer is required (got type float).  Implicit conversion to integers using __int__ is deprecated, and may be removed in a future version of Python.
  return QPixmap(':/images/MantidSplashScreen_4k.jpg').scaled(width * splash_screen_scaling
```
This makes the conversion to `int` explicit and squashed the warning.

Hahn, Steven authored Jan 29, 2021 and Peterson, Peter committed Feb 12, 2021

Signed-off-by: Steven Hahn <hahnse@ornl.gov>