Remove Ant and Gradle, replaced by Bazel

Now that Bazel rules are fully functional, remove Ant and Gradle configs
and the Gradle wrapper.

Also, update Travis to not use them anymore and update the developer
docs.

Fixes #180.

.travis.yml

@@ -35,9 +35,6 @@ install:
     sudo pip install Sphinx==1.1.3 &
     PIP_PID=$!
 
-    gradle getLibs &
-    GRADLE_PID=$!
-
     # Install Bazel.
     URL="https://github.com/bazelbuild/bazel/releases/download/${BAZEL_VERSION}/bazel-${BAZEL_VERSION}-installer-linux-x86_64.sh"
     wget -O install.sh -nv "${URL}"
@@ -48,17 +45,11 @@ install:
     # Wait for background processes to finish. All waits are necessary to make sure the exit status of each process is
     # checked.
     wait ${PIP_PID}
-    wait ${GRADLE_PID}
 script:
   - |
     # Fail if any of the following commands fails.
     set -e
 
-    # Ant-based tests: run unit-tests, build the web UI, build HTML+PDF docs.
-    ant test
-    ant gwtc
-    ant docs
-
     # Bazel-based tests: unit tests and building the JAR files.
     bazel test //src/test/java/org/edumips64/...:all
     bazel build //src/main/java/org/edumips64:standalone-jar --workspace_status_command=utils/bazel-stamp.sh --stamp