Implemented a workaround to address an issue that got introduced with Qt 5 on OS X (closes #138).
Fixed the issue with some special menu items on OS X (closes #163).
Minor improvements to our Help and CellMLModelRepository windows following the release of Qt 5.1.
Revert "Minor improvements to our Help and CellMLModelRepository windows following the release of Qt 5.1."

This reverts commit 3d643300434770e21d4b433b0b72391106d77a44.
Merge branch 'master' into issue31