Add boat spawner entries for downstream mission editing

[JKipers]

Just added boats to the vehicle_respawn_info.hpp so mission makers can place them in spawner in the future.

[dijksterhuis]

Have tested, all works beautifully.

A few minor naming convention things, happy to merge it, but would be good to get these suggestions added to clean it up.

[dijksterhuis]

PBRs have more firepower than the STAB rigs, so might make more sense to default them to a longer respawn time?

Suggested change

	RESPAWN_SHORT;
	RESPAWN_LONG;

[dijksterhuis]

These are all PBRs, so might make a bit more sense to have it like this

Suggested change

	class boat_small {
	name = "Small Boats";
	class boat_pbr {
	name = "Boats - PBR";

[dijksterhuis]

These are all nasty boats, so might make a bit more sense to have it like this

Suggested change

	class boat_large {
	name = "Large Boats";
	class boat_nasty {
	name = "Boats - Nasty";

[dijksterhuis]

These are all STAB boats, so might make a bit more sense to have it like this

Suggested change

	class boat_light {
	name = "Light Boats";
	class boat_stab {
	name = "Boats - STAB";

[dijksterhuis]

naming convention

Suggested change

	class small_transport {
	class pbr_m60 {

[dijksterhuis]

naming convention

Suggested change

	class large_boat_40mm {
	class nasty_40mm {

[dijksterhuis]

naming convention

Suggested change

	class light_transport_m2 {
	class stab_m2 {

[dijksterhuis]

naming convention

Suggested change

	class light_transport_m60 {
	class stab_m60 {

[dijksterhuis]

naming convention

Suggested change

	class light_transport_mk18 {
	class stab_mk18 {

[dijksterhuis]

Removal of empty space

Suggested change