Combine terrain reflection with terrain buffer

[Riot]

bonus: attempt to calculate when a reflected polygon's angle is such that it's invisible and don't add those to the buffer

[Riot]

make ads and corporation signs visible in water reflection, re #72

→ <<cset 212e7d180bf9>>

[Riot]

make water rendering buffer and shader based, re #72

→ <<cset 9bffb60ffa26>>

[Riot]

adding terrain reflection to terrain buffer, resolves #72

→ <<cset 4e56d2a01071>>