Merge remote branch 'origin/feature/7021_cmake_linux_distro'
Re #7027. Adding cmake option to enable qtassistant.
Merge remote-tracking branch 'origin/feature/7027_enable_qtassistant'
Merge remote-tracking branch 'origin/bugfix/7030_vsi_crash'
Fix plot axes not updating on OS X.

The issue seems to be with the 'from' and 'to' boxes. When you enter a
value and click apply then the box does not lose focus like on the other
platforms so the internal value does not get updated and when the dialog
asks what the value is it returns the original and not the new one.

An old comment suggests that the fix used to cause a crash but it no
longer seems to...

Refs #7036
Fix so that axes are updated on clicking ok.

There was a bug on the Mac also that meant a user would have to click apply
first and then okay to see any changes.
Refs #7036
Merge branch 'bugfix/7036_osx_plot_axes' into develop