[API] Fix dependency tree issue for imgui-java-app

resolve #75
resolve #127

Removed shadowing for `imgui-java-app.jar` which is published to Maven Central.
Shadow Jar now has a prefix `-all` - for those one who prefer to use raw jars instead dependencies in maven/gradle.

build.gradle

@@ -12,13 +12,6 @@ allprojects {
         mavenCentral()
     }
 
-    tasks.withType(JavaCompile).tap {
-        configureEach {
-            sourceCompatibility = JavaVersion.VERSION_1_8
-            targetCompatibility = JavaVersion.VERSION_1_8
-        }
-    }
-
     tasks.withType(Jar).tap {
         configureEach {
             from(project.rootDir) {