MAPS, WADS: Reworked e1m1

[Zungrysoft]

Description of Changes

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Significantly overhauled e1m1. Previously, e1m1 was too similar to the original game's e1m1, which set up an expectation that LibreQuake's singleplayer campaign was mostly just going to re-tread the same ground as the original game's campaign. Working with @RandomBrushes and @adaya, I have replaced several areas in the level with brand new combat. This PR also contains changes from @RandomBrushes, who made a bunch of detailing improvements to the map as well.

Changelog:

• Completely overhauled the first few combat encounters.
• Overhauled the Nailgun encounter.
• Changed the Double-Barelled Shotgun encounter by making the entire upper deck of the jail a secret area.
• Added force fields to the enemies on the upper deck. (credit: @RandomBrushes)
• Removed teleported enemies in the final encounter.
• New secrets and modifications to existing ones.
• Fixed unused intermission cams by making intermission cams depend on the number of found secrets.
• Minor gameplay tweaks to existing areas.
• Lots of lighting and texture adjustments. (credit: Myself and @RandomBrushes)
• Deathmatch support

Visual Sample

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Your view upon starting the level:

The train station:

The first combat encounter

The trainyard

The new nailgun area

Shotgun force-fields

Acid tunnel

Shortcut back to the start

Checklist

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• I have read the LibreQuake contribution guidelines
• I have thoroughly tested my changes to the best of my ability
• I confirm I have not contributed anything that would impact LibreQuake's licensing and usage
• This Pull Request fixes a critical issue that should be reviewed and merged as soon as possible

[RandomBrushes]

The build fails due to

WARNING: unable to find texture sky-test

[lavenderdotpet]

The build fails due to

WARNING: unable to find texture sky-test

approve this #188

[Nolcoz]

Its really good, ye

[RandomBrushes]

Looks good to me :-)