This reverts commit 55c385e96e6594ec1ac3b5cd41ccd2df6048b696, reversing
changes made to 61bb29d492.

JGit 4.0.0 fixes a memory leak but introduces a non-compatible change
for closing the RevWalk: before it was release() but now is close()

Also switch back to Maven Central repository.

This is a fairly functional variation of Gitblit with one notable
exception:

    The security filters are not working properly.

This is a design flaw in Guice that I have reported upstream [1].  The
general idea is that Guice-Servlet filters are not properly wrapping the
ServletRequest. This has historically been a problem for Guice-Servlet
servlets but Google has fixed most of those issues.  Unfortunately, all
the same flaws reported against the servlet delegation also exist in
Guice-Servlet filter delegation. :(

[1]: https://code.google.com/p/google-guice/issues/detail?id=807

The Jetty 9.2 quick start mechanism provides almost an order of
magnitude improvement in start time [1].

[1] https://webtide.com/jetty-9-quick-start/