Improving layout for wide screens. Issue #96.

[luigi-rosso]

I made the task columns not go over a certain width (currently corresponds to modal max width). This helps prevent the add task/bug buttons from getting too wide too. We can tweak this further if we want that column to be bigger than the archived tasks one.

One thing I ran into when implementing this was that I was unable to use a the constraints to achieve the layout I wanted, so I resorted to measuring the width, which isn't ideal.

I had originally tried to do it with constraints by using FlexFit.loose and constraining the width of the content. This works in constraining and aligning the columns properly, but the first column doesn't expand to the full remaining width.

Row(children:[ 
   // characters 
   Expanded(...), 

   // active tasks
   Flexible(
      fit: FlexFit.loose, 
      child: ConstrainedBox(...),
   ),

   // archived tasks
   Flexible(
      fit: FlexFit.loose, 
      child: ConstrainedBox(...),
   ),

Looks like this on an iPad Pro:

[efortuna]

does this container actually do anything? It doesn't like it has any height/width/color settings

[luigi-rosso]

Oversight, should've been removed! Thanks for catching.

[filiph]

LGTM