Use custom dependency resolution

- Use Apache Ivy to resolve artifact URLs
- Update build model with full artifact IDs
- Generate Maven module metadata to support dynamic version constraints
- Resolve snapshot versions and generate snapshot metadata
- Add test fixtures and rewrite Gradle plugin tests
- Update dependencies

fixtures/dependency/dynamic-snapshot/groovy/build.gradle

@@ -0,0 +1,12 @@
+plugins {
+    id 'java'
+}
+
+repositories {
+    jcenter()
+    maven { url 'https://jitpack.io' }
+}
+
+dependencies {
+    implementation 'com.github.anuken:packr:-SNAPSHOT'
+}