Dashmode tweaks

See merge request !646

- Remove the ability for non-SF_MACHINE players in dashmode to break spikes and monitors
- Replace instances of dashmode magic numbers with dashmode constants
- Add dashmode constants to dehacked.c

Fix NPC Amy's love hearts crashing if they didn't have a set fuse

See merge request !641

Add missing glseg checks (and remove a superfluous one)

See merge request !642

Reorder map loading

See merge request !635

Extra functionality for lua

See merge request !601

Fix mouse being grabbed even when not used

See merge request !639

The other way around this time.

This reverts commit 6c85c4e1.

Fix usage of V_GetColor

See merge request !638

Use GCC 8.1 for AppVeyor 64-bit builds

See merge request !624

Add clipboard functionality to the Connect via IP textbox.

See merge request !597

I was using V_GetColor in a lot of places I shouldn't have, making the game look wrong with a non-default colour profile.
Though, I left R_RainbowColormap alone.

Remove "z" from "vertex_t"

See merge request !636

Provide a fix for "non-sloped" slopes launch/land behavior by checking the normal's components.

See merge request !634

Adapt P_ClosestPointOnLine3D() to be much like FV3_ClosestPointOnLine() and use vector3_t's as args, save for the hypotenuse calculation, which remains the same; the output should be the same as before.
Adapt the rope hang snapping to the new function's form.

Move P_ProcessLinedefsAfterSidedefs into P_LoadMapData, but move map data copying after everything else

Compressing sidedefs can break both special effects and netgame syncing, so let's get rid of it

See merge request !628

Textmap parser

See merge request !604

Fix major issue

See merge request !625

Remove Direct Draw from AppVeyor config

See merge request !622

CV_FindVar for Lua

See merge request !583

Do not save netgame-synced console variables

See merge request !623