Update Issue/321

[Gamebuster19901]

• Removes some unused imports,
• Import/Export Animation Exceptions subclass IOException instead of Error
• Fixes a build error

The build error was the following:

gamebuster@gamebuster-System-Product-Name:~/Desktop/Modding/LitiEngine$ ./gradlew build

> Task :compileJava FAILED
/home/gamebuster/Desktop/Modding/LitiEngine/src/de/gurkenlabs/litiengine/graphics/animation/AsepriteHandler.java:270: error: cannot infer type arguments for HashMap<K,V>
        Map<String, Integer> frame = new HashMap<>() {{
                                                ^
  reason: cannot use '<>' with anonymous inner classes
  where K,V are type-variables:
    K extends Object declared in class HashMap
    V extends Object declared in class HashMap
/home/gamebuster/Desktop/Modding/LitiEngine/src/de/gurkenlabs/litiengine/graphics/animation/AsepriteHandler.java:276: error: cannot infer type arguments for HashMap<K,V>
        Map<String, Integer> spriteSourceSize = new HashMap<>() {{
                                                           ^
  reason: cannot use '<>' with anonymous inner classes
  where K,V are type-variables:
    K extends Object declared in class HashMap
    V extends Object declared in class HashMap
/home/gamebuster/Desktop/Modding/LitiEngine/src/de/gurkenlabs/litiengine/graphics/animation/AsepriteHandler.java:282: error: cannot infer type arguments for HashMap<K,V>
        Map<String, Integer> sourceSize = new HashMap<>() {{
                                                     ^
  reason: cannot use '<>' with anonymous inner classes
  where K,V are type-variables:
    K extends Object declared in class HashMap
    V extends Object declared in class HashMap
/home/gamebuster/Desktop/Modding/LitiEngine/src/de/gurkenlabs/litiengine/graphics/animation/AsepriteHandler.java:301: error: cannot infer type arguments for HashMap<K,V>
    Map<String, Integer> size = new HashMap<>() {{
                                           ^
  reason: cannot use '<>' with anonymous inner classes
  where K,V are type-variables:
    K extends Object declared in class HashMap
    V extends Object declared in class HashMap
4 errors

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileJava'.
> Compilation failed; see the compiler error output for details.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 552ms
3 actionable tasks: 2 executed, 1 up-to-date

[nwessman]

LGTM! Thanks for the fix!