A slick-looking LightDM greeter.

Features:
- Slick-Greeter is cross-distribution and should work pretty much anywhere.
- All panel applets are embedded. No external indicators are launched or loaded
  by the greeter.
- No settings daemon are launched or loaded by the greeter.
- This greeter supports HiDPI.
- Sessions are validated. If a default/chosen session isn't present on the
  system, the greeter scans for known sessions in /usr/share/xsessions and
  replaces the invalid session choice with a valid session.
- You can take a screenshot by pressing PrintScrn. The screenshot is saved in
  /var/lib/lightdm/Screenshot.png.
- The default configuration is stored in dconf under the schema
  x.dm.slick-greeter.
- Users can create and modify /etc/lightdm/slick-greeter.conf, settings in this
  files take priority and overwrite dconf settings.