Fix bumpcode, fix magnet landing (better fix)

See merge request KartKrew/Kart-Public!281

Server Gametype Preference

See merge request KartKrew/Kart-Public!278

Fail loudly when config isn't writable

See merge request KartKrew/Kart-Public!279

The intent is to stop servers from needing to dedicate their limited name/MOTD space to things like advertising `lessbattlevotes`, and to avoid "punishing" a server in visibility for allowing temporary gametype switches. However, this is possibly a controversial change, so I'm doing it in its own commit in case there's a clear consensus to revert.

* A "canon" adaptation of the community-created server option `lessbattlevotes`.
* If set to "None", voting behaves as before.
* If set to "Race" or "Battle". that gametype is considered the preference.
    * The voting screen is always operated from the perspective of the preferred gametype.
    * If you're in an un-preferred gametype, the third vote option will always allow you to continue the gametype.
    * If the preferred gametype is Race and you've just exited a Battle map, Encore may now appear on the second vote option.
* A number of bugs with voting have been corrected.
    * If `kartencore` is on, the third vote option will now correctly have Encore applied.
    * If a custom EXE or malformed packet sends an Encore flag alongside a Battle gametype ID, actively strip it.
        * Just to note, clients do not enter Battle Encore with or without this change - this just prevents a promise the rest of the game couldn't fulfill.

Add warning and reset flow for non-default masterserver address

See merge request KartKrew/Kart-Public!277

backport P_CheckSight from vanilla

See merge request KartKrew/Kart-Public!273

2.2 Backports - add ceil slope double step-up/down and fix sprite/models all black in sector with light level of 256

See merge request KartKrew/Kart-Public!274

Uncapped

See merge request KartKrew/Kart-Public!276

Makes the displayed FPS more accurate to what it's actually displaying.

Also removed HUDTRANS from it -- stop it fading out during level transitions, it's annoying when I actually want to see the FPS during those bits.

Fixes KartKrew/Kart-Public#10

Was done this way for the sake of an older version of uncapped's timing; now that the new timing is much better, I decided it should remain as close to pre-uncapped as it can be.

Advertise_OnChange is CV_NETVAR, so the server will get registered by CV_LoadNetVars when the server starts.

This race condition occasionally pops up in master, but got very consistent with uncapped.