Added 'minimalistic' test.

slf4j and logback were already used in ExoneraTor.  This commit makes all
classes use slf4j and replaced j.u.l and System.{err,out} logging.

Also added test sources to checkstyle target.

This includes separating a utils class and also moving all Gson/JSON
related code into QueryResponse for better encapsulation.
Adding Exit enum.

We don't expect results to be in order, and taking out ORDER BY
statements means we don't need to worry about replacing numbers with
names for better readability.

Make it more explicit which query response versions we accept, and log
a proper warning if we receive a version we don't accept.

Catch RuntimeException when reading the query response, also to catch
anything that comes from Gson.

Hard-code exoneraTorHost rather than reading it from web.xml.

Implements #16596.

This prepares splitting up ExoneraTor into front-end and back-end.

Note that some code duplication between ExoneraTorServlet and
QueryServlet was deemed acceptable, because ExoneraTorServlet will be
moved to metrics-web in the medium term anyway.

This is another prerequisite for changing queries towards making a
single query per request (#16596) and towards splitting up ExoneraTor
into front-end and back-end.

 1: Parse the request.
 2: Query the database.
 3: Write the response.

This doesn't just clean up code, it's also a prerequisite for changing
queries towards making a single query per request (#16596).

Implements #22811.

Implements #22682.

Language names and translations of "This page is also available in the
following languages:" taken from https://www.debian.org/.

Apparently, the zero-width space character causes trouble when copying
and pasting fingerprints.  Fortunately, we can let the fingerprint
break anywhere using CSS.

Fixes #17231.

Implements #21535.

Removed obsolete git-submodule.

We're using metrics-lib for downloading descriptors from CollecTor,
but we're still using our own parsing code.  Let's avoid duplicating
code by using what metrics-lib provides.

Upgrade to metrics-lib 1.4.0 and include newly required logging .jar
files.

Include PostgreSQL .jar file in the .war file rather than relying on
Tomcat to provide it.

Turns out that resource bundles must be ISO 8859-1 encoded, so we'll
have to convert the German file using:

  native2ascii -encoding UTF-8 old new

Also make some minor changes to make UTF-8 encoding of the resulting
web page more explicit, and correct the included language code.

Fixes #19954.

Fix typo "ant" to "and" and add   to the end of all sentences.

Both tweaks suggested by John Lorenz.

Required changes from previous schema:
 - CREATE OR REPLACE FUNCTION insert_statusentry [...];
 - CREATE OR REPLACE FUNCTION insert_exitlistentry [...];
 - ALTER TABLE statusentry DROP COLUMN descriptor;
 - ALTER TABLE exitlistentry DROP COLUMN rawexitlistentry;