Allow layouts to be responsive with defined breakpoints

[stuartlynn]

Allow different layouts to be used at different breakpoints. Sample API containers could look like the following where L,M and S are three defined breakpoints.

{
  layout:{
   L: Grid:{},
   M: Linear:{}
   S: Linear:{}
},
panes: []

Add some sane defaults for this. Allow users to configure breakpoints at the top application level but similarly have sane defaults

[nofurtherinformation]

From #111

Responsive design changes layout and sizing choices based on the size of the screen viewing the context. A mulit-column layout might shifting into a single column layout, font sizes change, tooltips change to modals, etc.

Most of the layout sizing parameters will need the option for breakpoint-based responsive parameters. Here's what we'll need to do:

• [ ] Implement default breakpoints and access to those in the global state or context
• [ ] Enable options for custom breakpoints in the spec
• [ ] Add pane editor options for any sizing or pixel based measurements based on responsive breakpoints
• [ ] Create sane defaults for how to smartly manage responsive layouts if users do not select any options