Per-shield banner colors

[ZeLonewolf]

Fixes #357

This PR allows the style to specify the color of a shield's banner on a per-shield basis. If set, the color will apply to all banners on a shield. Additionally, the style can specify the halo knockout color on a per-shield basis.

Additionally:

• Banner rendering code was consolidated into a new file, shield_banner.ts, for improved code navigation and readability.
• Banner colors were implemented for Vermont alternate routes (green) and US Numbered Highway System historic routes (brown).

Samples:

[claysmalley]

Off the top of my head, these other networks should be changed as well:

• GLCT:Loop, brown
• US:CA:Business, green
• US:MD:Business, green
• US:NJ:ACE:Connector, blue
• US:NJ:CR:Spur, blue
• US:NJ:CR:Truck, blue
• US:OH:ASD:TWP, green
• US:OH:ATH:Trimble, green
• US:OH:MED:York, blue
• US:OH:PAU:Latty, green
• US:OH:PAU:Washington, green
• US:OH:WAS:Aurelius, green
• US:OH:WAS:Salem, green
• US:SC:Truck, blue
• US:SC:Business, blue
• US:SC:Alternate, blue
• US:TX:Recreational, brown
• US:TX:Express:Toll, blue
• US:TX:Loop:Toll, blue
• US:TX:Loop:Express:Toll, blue
• US:TX:CTRMA:Express, blue
• US:TX:Jackson, blue
• US:TX:Andrews:Andrews:Loop, blue
• AU:*:ALT, green
• AU:*:ALT_S, blue

[ZeLonewolf]

I've added all the listed banners except for the Ohio ones because that code is complicated. #943 documents updating the Ohio shield banners to the right colors.

[claysmalley]

Fine by me.