Compile with wlroots 0.15.1

This release contains the following two breaking changes:

1. Disabling outputs now causes views to be re-arranged, so in the
   context of idle system power management (for example when using
   swaylock), it is no longer suitable to call wlr-randr {--off,--on}
   to enable/disable outputs.

2. The "Drag" mouse-event and the unmaximize-on-move feature require
   slightly different `<mousebind>` settings to feel natural, so suggest
   updating any local `rc.xml` settings in accordance with
   `docs/rc.xml.all`

As usual, this release contains a bunch of fixes and improvements, of
which the most notable feature-type changes are listed below. A big
thank you to @ARDiDo, @Consolatis and @jlindgren90 for much of the hard
work.

- Render overlay layer popups to support sfwbar (issue #239)

- Support HiDPI on-screen-display images for outputs with different scales

- Reload environment variables on SIGHUPi (issue #227)

- Add client menu

- Allow applications to start in fullscreen

- Add config option `<core><cycleViewPreview>` to preview the contents
  of each view when cycling through them (for example using alt-tab).

- Allow mouse movements to trigger SnapToEdge. When dragging a view, move
  the cursor outside an output to snap in that direction.

- Unmaximize on Move

- Support wlroots environment variable WLR_{WL,X11}_OUTPUTS for running
  in running nested in X11 or a wlroots compositor.

- Support pointer gestures (pinch/swipe)

- Adjust views to account for output layout changes

Full `git shortlog` below

ARDiDo (12):
      decorations: use view_apply_maximized_geometry instead of view_maximize
      fullscreen: ignore decorations and maximize requests while fullscreen
      Prevent views from starting in fullscreen
      mouse: add support for drag mouse event
      labwc-config: fix spelling mistake
      mousebindings: change default focus and raise to press from drag.
      mousebindings: use available resize edges first in drag actions
      xdg: Allow wayland applications to start in fullscreen
      xwayland: Allow xorg applications to start in fullscreen
      CSD: Fix no fullscreen at startup in some applications without ssd
      OSD: Scale OSD to the largest output scale
      OSD: Use separate OSD texture for each output

Consolatis (18):
      config/keybind.c: Don't overwrite the stack
      Rewrite action handling to allow multiple actions at once
      More robust rc.xml parsing
      Unmaximize on Move
      Allow mouse movements to trigger SnapToEdge
      CodeStyle
      Short term solution to prevent segfaulting on TTY switch. See #206.
      Centralize freeing of action lists
      config/rcxml: Prevent overwriting action argument
      src/ssd.c: Clarify button dimension calculations
      Add window menu
      Add WindowMenu button
      src/output.c: fix debug flag for full frame damage
      Move is_button() into src/ssd.c and make it public
      Use proper enum argument type for desktop_surface_and_view_at
      src/cursor.c: Reduce damage on button hover detection
      Add missing docs for mouse window snapping
      Reload environment on SIGHUP. Partly fixes #227

Johan Malm (19):
      Update NEWS.md
      README.md: update acceptance criteria URL
      keyboard: cancel repeat when handling key-bind
      cursor.c: fix coding style
      desktop: simplify desktop_focus_and_activate_view()
      docs/autostart: remove wlr-randr {--off,--on}
      wlroots.wrap: add .git to url to avoid redirection warning
      action.{c,h}: fix coding style
      Move action() prototype from labwc.h to action.h
      seat: support WLR_{WL,X11}_OUTPUTS >= 2
      view: fix bug in view_snap_to_edge()
      view: adjust views safety following layout change
      desktop: correctly forward cursor motion-event to layer-popup surfaces
      ssd: do not render resize cursors over exclusive layer-shell clients
      ssd: revert last commit
      cursor: revert 6651d; remove cursor_update_focus()
      cursor: cursor_rebase() on mouse scroll
      wlroots.wrap: use 0.15.1
      output: render overlay lay popups

John Lindgren (4):
      Adjust views to account for output layout changes
      cursor: Don't allow a DRAG action to start from a double-click
      cursor: More reliably clear "pressed" status of mouse bindings
      view: Handle maximized view on disabled output more simply

Liam Middlebrook (1):
      output: Add option to preview the contents of the current cycle_view

Michael Weiss (1):
      build: Relax the version constraint for wlroots to accept patch releases

bi4k8 (2):
      factor keyboard/cursor cleanup into own functions
      cursor: support pointer gestures (pinch/swipe)

hype3 (2):
      Update README.md
      Update README.md