layout - First pass at moving to css flexbox layout

[jeremychone]

Problem

Today we are using "position: absolute" for application layout (where height is constraints as well), however, this way of doing application HTML layout is more a workaround for old HTML/CSS browsers that did not support the flexbox layout which has been designed for this purpose.

Solution

We should be moving to css boxlayout.

Note

The only catch of this approach is that it does not work well in older version of IE (IE 10), but is relatively well supported in all other browsers including mobile ones (see caniuse.com/#search=flexbox