Fix tooltips z-index in motions flow

[arrenv]

Steps to reproduce

1. Create an action with the Reputation decision method.
2. Hover over one of the stage pills in the motion flow panel.
3. You will notice that you can not read any of the tooltips.

Expected behaviour

• The tooltips should be visible.

Be sure to check that the tooltips and pills don't overlap other elements that should have a higher z-index, such as the the Userhub, as previously raised and resolve in this issue https://github.com/JoinColony/colonyCDapp/issues/2277.

Actual behaviour

• Tooltips in the motion flow are hidden behind the adjacent content panel.

[AdrianDudko]

@arrenv this should be fixed in another PR - @CzarekDryl will link that PR.