Improve compatibility for DarkRP and TTT

[rbreslow]

Overview

• Add SpeakPreParseChatText hook so compatibility layers can manipulate the object that is passed to speak.ParseChatText
• Add SpeakShouldShowTag hook so compatibility layers can decide whether or not it is appropriate to show a chat tag
• If the element prior to a Player element is a Color then prefer that to style the player's name over team.GetColor (for TTT compatibility, which only has 1 team)
• Add tag_enabled preference to specify whether to show tags at all
• I18n.Set now takes a third argument allowing you to define for translations other than the active locale
• Rewrite DarkRP compatibility
• Add TTT compatibility

Connects #14

Testing Instructions

I downloaded DarkRP and then applied the following diff:

diff --git a/docker-compose.yml b/docker-compose.yml
index 4998d45..8f26363 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -4,6 +4,7 @@ services:
     image: quay.io/rbreslow/garrysmodds:slim
     volumes:
       - ./src/speak:/var/lib/steam/.steam/SteamApps/common/GarrysModDS/garrysmod/addons/speak
+      - ~/Downloads/DarkRP-master:/var/lib/steam/.steam/SteamApps/common/GarrysModDS/garrysmod/gamemodes/darkrp
     tty: true
     ports:
       - "27015:27015"

Then, after running ./scripts/server, switch to DarkRP:

gamemode darkrp
Changing gamemode to DarkRP (darkrp)
changelevel gm_construct

See that the compatibility layer works as intended:

Switch to Trouble in Terrorist Town:

gamemode terrortown
Changing gamemode to Trouble in Terrorist Town (terrortown)
changelevel gm_construct

See that the compatibility layer works as intended:

[rbreslow]

Added you guys again if you're interested in taking a look. This might be more interesting than the VGUI changes in my last PR. No pressure to review.