Split CC:T into common and forge projects

After several weeks of carefully arranging ribbons, we pull the string
and end up with, ... a bit of a messy bow. There were still some things
I'd missed.

 - Split the mod into a common (vanilla-only) project and Forge-specific
   project. This gives us room to add Fabric support later on.

 - Split the project into main/client source sets. This is not currently
   statically checked: we'll do that soon.

 - Rename block/item/tile entities to use suffixes rather than prefixes.

buildSrc/src/main/kotlin/cc/tweaked/gradle/Extensions.kt

@@ -7,6 +7,9 @@ fun DependencyHandler.annotationProcessorEverywhere(dep: Any) {
     add("compileOnly", dep)
     add("annotationProcessor", dep)
 
+    add("clientCompileOnly", dep)
+    add("clientAnnotationProcessor", dep)
+
     add("testCompileOnly", dep)
     add("testAnnotationProcessor", dep)
 }