UP-4205 Add and map Filter blocking CVE-2014-4172 .

Adds a Filter for sanitizing request parameters and configures this Filter to block `CVE-2014-4172`, an illicit proxy vulnerability in the Java CAS Client version included with uPortal releases and present on the uPortal 4.0 patches branch.

Tracked in JIRA at [UP-4205](https://issues.jasig.org/browse/UP-4205).

This Filter blocks the vulnerability and is an alternative to addressing this issue with more change (namely, upgrade to Java CAS Client v 3.3, which has different dependencies and slightly different configuration than the Java CAS Client 3.2 in use in uPortal 4.0.).

This Filter is a fork of and application of https://github.com/Jasig/cas-server-security-filter/pull/6 .  Including the Filter directly in the uPortal codebase prevents having to modify `pom.xml` to pull in new or different dependencies (and allows uPortal not to wait for this Filter to appear in a dependency available from Maven Central).
Does seem like there ought to be common code to factor out.  

I suspect there isn't actually common code to factor out, in part because the test cases class has broadly two kinds of tests in it (tests for the Filter as a whole, and tests for the individual stateless static methods).  The tests for the Filter are heavier and require more set up, but externalizing that set up into an `@Before` would incur that setup on every test method, even methods that don't need that setup.

Splitting the test cases class into two, one for each type of test and so enjoying different `@Before` methods, might allow for focusing the common setup for each type of test, but even in the heavier tests for the `Filter` as a whole, there's a limit to what's common since part of what the tests are doing is feeding it different environmental configuration each time.

Early in the development of this Filter there was an `@Before` setup method.  I [refactored it out](https://github.com/apetro/cas-server-security-filter/commit/0461b48e28133eea4065deb36b158c3fb8ccd6ac) because it didn't seem to be helping.

In any case, opportunity to refactor the unit tests in the future, but I'm not keen on making that refactor at this juncture.