The rendering code doesn't use the exclusive input surface at all
anymore to decide to skip rendering of shell surfaces. This fixes
a weird situation in which a client requests exclusive input but
isn't an overlay layer surface.
The renderer also renders all overlay surfaces in this situation,
not just one. This simplifies the code and fixes rendering when
there are more than one overlay surfaces (e.g. for a virtual
keyboard to type the lockscreen password).
Introduces a command to manually set urgency, as well as rendering of
urgent views, sending the IPC event, removing urgency after focused for
one second, and matching urgent views via criteria.
Rather than maintain copies of the entire focus stack, this PR
transactionises the focus by introducing two new properties to the
container state and using those when rendering.
* `bool focused` means this container has actual focus. Only one
container should have this equalling true in its current state.
* `struct sway_container *focus_inactive_child` points to the immediate
child that was most recently focused (eg. for tabbed and stacked
containers).
We currently have several ways of setting debug flags, including command
line arguments, environment variables, and compile-time macros. This
replaces the lot with command line flags.
