Changes made to the starmap screen fleet arrows

[hemoridos]

• Replaced the line drawn between fleets and it's targets with a arrow similar to the one in the original.
• Changed the color of the movement arrow to be the same as the original.
• Increased the line's thickness to 1.5 for better visibility.

Fixed some java8 related compiler issue.

Attached some pictures of the new arrows and one with the original.
The arrow does not scale with zooming in or out.
Original IG:

Changed in open-IG:

[akarnokd]

Why did you need that Java 8 change?

[hemoridos]

Apparently since java8 these method signatures are considered ambiguous and the compiler throws an error about it:
public void add(Trait t) public void add(Iterable<? extends Trait> ts)

The problematic method call is here in SkirmishDefinition,java:56:
sp.traits.addAll(traits.trait(xtrait.get("id")));
When the compiler sees the generic type returned by the traits.trait method, for some reason it also matches it with the generic parameter in public void add(Iterable<? extends Trait> ts)

The jdk I used is the one bundled with eclipse. jdk-17.0.8.101

[hemoridos]

Added a commit without typecasting. Simply changed the add(Iterable...) to addAll(iterable...)