Flag tweaks in configurations

- The Doom format "multiplayer" flag is "multiplayer-only", i.e., "not
single".
- According to my Random House Webster's, "impassible" is "incapable of
suffering pain or harm, incapable of showing emotion, impassive", so
replaced those by "impassable" which is "not allowing passage over,
through, along, etc.".
Added pusher and puller icons for Boom things.
Allow parser to call tokenizer debug mode.
Reorganized thing groups a bit.

Invisible things like map spots, polyobject points, slope effects, etc.
go into parent group "Special Effects", dead things and tortured bodies
go into parent group "Gore", decorations are categorized into themes.
Added waterzone prop to ZDoom UDMF.
Fix one Hexen flag.
Work on game configs.

- DECORATE parser now interprets translations correctly.
- Added $Group keyword to DECORATE parser, as an alternative to DB's
"category".
- DECORATE $keyword values are read to the end of the line, even if
unquoted, for compatibility with DB2.
- Added special handling for TNT1A sprites.
Make texture browser insist a bit more.

When opening it, the current texture was claiming to have unknown size,
until clicking away and back.
Great purge of unneeded S_FMT macros
Tokenizer change for GameConfiguration change.

Forgot to commit it.
Display line flags except for UDMF format.

UDMF will need a different method for those.
MapCanvas should tell when it handles actions.

Cut down on the untrue warning spam about unhandled actions that were
actually handled.
Merge branch 'master' of https://github.com/sirjuddington/SLADE
Repair my old TC's embedded config.

- Allow to remove undesired old things from config.
- Let embedded configs have a "game" section
- Don't let raw DECORATE code (without //$keywords) override
configurated things.
Remove some dead code.
RunDialog would crash without a base resource.
Hexen config: use default textures that exist.

Instead of copying the defaults from Heretic.
Eternity config: added the nightmare spectre thing.
Added ability to read translation tables

Used notably by Hexen.
Found some text lumps that failed to open.

Added a workaround in case they are encountered.