Re #6902. Remove a hard coded path.

The one used for linux will give the right answer in a more general way
and will avoid looking into an installed Mantid when running a locally
built one.
Re #6902. Remove unnecessary code from linux build.

We use system-installed sip & PyQt on linux.
Revert "Re #6902. Remove unnecessary code from linux build."

This appears to have had a bad effect on our fragile MantidPlot
python tests and I'm not inclined to figure out what's wrong
exactly (they still work locally for me).

This reverts commit 424a87b8fd794b5573ac709a527a02b291f9f604.
Re #6803. Greatly improve unit test coverage for DataService.

Some tests fail at the moment due to defects with the class under test.
Re #6803. Don't suppress notifications for hidden objects/workspaces.

This may change the behaviour of the workspace dock, but then it was
broken anyway.
Re #6803. Getter methods for DataService contents exclude hidden.

size(), getObjectNames() & getObjects() exclude hidden objects/workspaces.
This will mainly affect corresponding python methods.
Re #6803. Fix DataService test.
re #6992 fix attempt for severity level error
re #6992 fix attempt for performance level error batch 1
re #6992 fix attempt for performance level error batch 2
re #6992 fix attempt for performance level error batch 3
re #6992 fix attempt for style level, and a bug fix
re #6992 more style level fixes, and a bug fix
re #6992 revert chages to DetectoEfficiencyCorUser.cpp
Re #6803. Have getter methods depend on 'hidden' settings.

Amend size(), getObjectNames() & getObjects() to include 'hidden'
objects if the corresponding ConfigService setting (MantidOptions.InvisibleWorkspaces)
is set to true (1).
Merge remote-tracking branch 'origin/feature/6902_built_and_installed_on_osx'
Re #6803. Factor out a bunch of repeated boilerplate stuff.
Re #6803. Add tests for 'hidden' WS behaviour.

The ADS is where this functionality is mainly (only?) used, so these tests
have been added to make sure the methods are not overridden.
Re #6803 Remove entirely unused code.
Re #6803. Add method that always includes hidden objects.