Bug fix for adding marker to experience

The experience was not being set on the view controller so validation
of the code always failed preventing the user from adding a new
code/marker.
Added help text for adding marker

Added some text on the “add marker” screen to display problems with the
entered code.
Edited [Experience isValid/isKeyValid] to give a reason when a code is
not valid.
Bug fix for marker outline

Outline would appear in wrong place on devices that do not use the full
screen width for detection (introduced by commit: 9fbe94e).