Add option for fields to follow on in the same row from previous fields

[matthewhorridge]

The column based UI can feel akward for some things, with lots of wasted space.

I'd like an option to say that a field should be on the same row as the previous field. So it looks like this.

This could be supported with a simple boolean field in the _ui element of the model 'continuePreviousRow' : true

FYI I just added flex-box with two lines of CSS for the above (display: flex; flex-direction: row)

Could be even nicer if you could weight the fields in size: