Rework textmap parser to always read a parameter's value, even if it doesn't recognize the parameter

Setup repeatcnt in P_LoadSidedefs instead of P_ProcessLinedefsWithSidedefs, since UDMF can set it directly

-Fix P_InitializeSector being called too early (band-aid fix for now, will reorganize this properly later)

Make P_LoadMapData() a return a boolean as well as P_LoadMapFromFile(); if they fail to load, they return false, and thus P_SetupLevel() will also return false.
TextmapCount() also now returns false if brackets are left open inside a textmap.

Fix saloon doors not letting players through when marked with the Ambush flag

See merge request !600

Fix fuckup

See merge request !598

New node formats

See merge request !595

Revert "Pass along virtnodes to extended nodes loading functions to make sure virtnodes->data is moved correctly"

This reverts commit cfc64285.

Pass along virtnodes to extended nodes loading functions to make sure virtnodes->data is moved correctly

P_GetNodetype: The virtnodes pointer is supposed to be the output parameter, so we have to pass a pointer to that pointer