Removes rooms, replaced with cv_advertise and "Advertise" on the host menu.

According to the new API, SRB2APPLICATION is sent instead of MODID. A contact
field was added, but there is no means of accessing it or setting it.

As a slight change, the server list will be populated even on an outdated
version of the game. (The new API was designed with this in mind.) The update
alert is still presented first of course.

Previously sounds with an origin would always start at max volume. This is
because the distance calculation adjusts the volume, and that volume needs to
be updated every tic as distance changes. Storing the original volume works.

- Far more inclined to give you Orbinaut, Jawz, Invincibility, and Grow. Far less inclined to give you Bananas or Sneakers.
- Item odds no longer scale with bumper count differences.

Cause more issues than fixes. Still around for Linux.

A and B are v2 terminology

(cherry picked from commit 679bfa21edec6b652def93082da5586e6c755678)

(cherry picked from commit 1f38db46298181d117432e12e88b326a92b4b785)

Attach initial join discord info to servercfg, so that we don't have a pause from needing to also send XD_DISCORD

XD_DISCORD is now reserved for when the options are changed mid-game

- Call DRPC_Init at the end of D_SRB2Main instead of in the middle
- Call Discord_RunCallbacks in D_SRB2Loop instead of G_Ticker
- Fix errorcount nums in I_Error, an old leftover from when Discord_Shutdown was not handled by I_AddExitFunction