v1.2.20.1: Internalize the welcome splash, welcome_splash.h

No longer streaming from the yailsrv. Initializing the memory used as the "framebuffer" with the welcome splash image. No longer need to clear on startup.

In the original commit I forgot to include the welcom_splash.h file. This fixes it.

Full Changelog: v1.3.4...v1.2.20.1