Allow to control opacity of direct children of ActiveStoryItem in Edit mode

[birbilis]

Version: 0.7.1

Since direct children of ActiveStoryItem (the ones shown in single-line boxes) are disabled, they're shown by default (FireMonkey library's behavior) as semi-transparent

To see how they will appear one has to exit Edit mode temporarily and enter back into it to continue editing

An alternative could be to have a slider in Edit mode to control that opacity (maybe at a side pane with app settings, but easy to access), since this is configurable (see https://stackoverflow.com/questions/34054415/how-can-i-keep-my-disabled-controls-opaque). The slider should cause instant change so that one can see the effect. Else could have a checkbox to toggle between using transparency or not