Dissolve top level gitiles-* directories

The current layout of having gitiles-* directories with separate java
source trees dates back to the bad era of Maven, when this specific
layout was necessary to decompose the build into separate pom.xml files.

Moreover, src/{main,test}/java are also Maven artifacts, so that we go
even further and create three top level directories:

* java
* javatests
* resources

Change-Id: I4421096428db1e3de019a9b6c1253217cf7e4fbe

BUILD

diff --git a/BUILD b/BUILD
index 773eb61..d65fe65 100644
--- a/BUILD
+++ b/BUILD
@@ -2,12 +2,12 @@
 
 pkg_war(
     name = "gitiles",
-    context = ["//gitiles-servlet:webassets"],
+    context = ["//resources/com/google/gitiles:webassets"],
     libs = [
-        "//gitiles-servlet:servlet",
         "//lib/jetty:server",
         "//lib/jetty:servlet",
         "//lib/slf4j:slf4j-simple",
+        "//java/com/google/gitiles:servlet",
     ],
-    web_xml = "//gitiles-war:web_xml",
+    web_xml = "//resources:web_xml",
 )