Adds shared pom.xml and google-checks.xml. I also add a test directory
to check that the pom works / is well-formed.

Add Travis configuration.

Remove unnecessary properties.

Ignore JavaDoc rules in test classes.

Ignore service account file.

Remove extra XML stuff from POM.

Subtrees are the primary way I expect people to use the
`java-repo-tools` repository. Since it's not a super common workflow, I
document the needed steps in the README.

Add instructions for using with subtrees.

I modify the checkstyle config to have SAME_PACKAGE imports appear
before third-party imports. I think this better matches the intent of
the import ordering rules in the style guide.
https://google.github.io/styleguide/javaguide.html#s3.3.3-import-ordering-and-spacing
Expecially since it says the `com.google` imports only appear after
static imports if the source file is in the `com.google` package space.

(cherry picked from commit 7ca0e7564d4d1a39714d8c90e71d5e408f30f4da)

Checkstyle: have SAME_PACKAGE imports appear before third-party imports

The pulling changes from Java Repository Tools instructions can now be followed verbatim.

The instructions here are much easier to follow and avoid unnecessary conflicts: https://help.github.com/articles/about-git-subtree-merges/

* Moved some checkstyle modules to java-repo-tools
* Moved some lines in .gitignore to the top level

Also update checkstyle to allow 1-letter variable names, since it
doesn't make sense to give long names to something like "arbitrary
column A that doesn't actually mean anything".

Samples are moved from:
https://cloud.google.com/appengine/docs/java/datastore/indexes

Note: I add a new script `test-devserver.sh` to the testing config. This
script runs the `mvn appengine:devserver` plugin, waits for it to start,
then verifies that it gets a non-error response from the `/` path. I use
this to verify that the `datastore-indexes.xml` files are correct (by
disabling autoGenerate, the local devserver throws an error when a query
is used without the correct index defined, just as production does).

We should probably add any "hello world" or other projects to this
check, as well. Anywhere we say to run `mvn appengine:devserver`, it
would be good to test that it is correct.

…e-from-java-docs-samples

Java repo tools update from java docs samples

This is an example of using the java-repo-tools parent pom in a sample.

To fix indentation and other simple errors, I ran the google-java-format
tool. https://github.com/google/google-java-format I still had to fix
imports, variable name, and javadoc checkstyle errors by hand.