Initial import of the geogit-geoserver plugin.

The geogit-geoserver plugin enables the configuration of geogit repositories
as GeoServer data stores, and geogit feature type trees as GeoServer layers.

It also exposes the geogit web api at <geoserver base address>/geogit (e.g.
http://localhost:8080/geoserver/geogit)

Or to a specific repository at <geoserver base address/geogit/<repository>,
where <repository> is given by the <workspace:store> name as configured
in GeoServer as a data store.
Added maven shade plugin configuration to create a shaded jar plugin

mvn install or mvn package will create target/gs-geogit-<version>-shaded-plugin.jar
which contains everything the plugin needs to work that's not already
provided by geoserver, plus some dependencies are "relocated" to avoid
clashes where geoserver has the same dependency but for a different
version.
Adapt geogit-geoserver to changes in geogit web-api as of geogit commit e1d82da5d0

In geogit changes were made to web-api in order to remove code duplication
between the geogit web-app module and this plugin. This commit removes
all the duplicated classes and leaves only the ones needed to reuse all
the web commands from geogit web-api (i.e. CatalogRepositoryProvider)
tweaks to the maven shade plugin settings
adapt to geogit test set up making <tmp dir>/repo the current working directory
Disabling embedded mongo tests for now
avoid carrying over geotools dependencies from geogit when the version used by geogit differs from the one used by geoserver-exts
Updated upstream geoserver dependencies to include gs-prefix.

Also including some upstream module name changes.
switch to use include patterns instead of excludes for the shaded jar (both can't be used)
Updated upstream geoserver dependencies to include gs-prefix.
Merge pull request #43 from groldan/geogit-geoserver-2.5

Geogit geoserver plugin for GeoServer 2.5
do not include logback in the geogit plugin.
no need of a direct dependency on guava
remove explicit xstream dependency from gsr

Needed to update the version of xstream to resolve test failures.
Xstream gets pulled in transitively, so instead of explicitly pegging a
version, use the one that gets pulled in instead.
resolve Closeables.closeQuietly deprecation issues

Use recommended Closer pattern instead of Closeables.closeQuietly.
add baseurl configuration for mapmeter

A baseurl config property makes it easier to change the host that all
mapmeter messages get sent to.