decision for whether or not a pane should be drawn out of the layout code and
into the redraw code.
This is needed for the new layout design, getting it in now to make that easier
to work on.
- change the one layout function into two _refresh and _resize
- create layout-manual.c for manual layout code
- move the fit panes/update panes code from window.c to the new file as it is only used by manual layout now
- move the resize pane code into layout-manual.c as well
- get rid of the direct calls to fit/update and make them go through layout
- rename a couple of variables
This is mainly as a first step before reworking the manual layout code to see if anything breaks.
