Before, loading a module would be guarded by an optional platform
condition. This made it possible to avoid loading and evaluating a
module if it did not support the host platform.
Unfortunately, this made it impossible to share a single configuration
between GNU/Linux and Darwin hosts, which some wish to do.
This removes the conditional load and instead inserts host platform
assertions in the modules that are platform specific.
Fixes#1906
* i3, sway: extract border functionality to common function
Converted the i3 module to use default_border and
default_floating_border and extracted that functionality out to be
shared between the i3 and sway modules.
* i3: add sumnerevans as maintainer
