Fix broken build from JGLFontRenderer API change.

Problem:

- The JGLFontRenderer API changed the beforeRender method by adding a
customRenderState Object parameter.

- This broke the latest Nifty 1.4-SNAPSHOT build.

Solution:

- Add customRenderState Object parameter to beforeRender method in private
inner class BatchRenderDevice.FontRenderer.

- No functionality has been added to support this parameter, so for now it
is simply unused.

Details:

Error message:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.3.2:compile (default-compile) on project nifty: Compilation failure: Compilation failure:
[ERROR] nifty-gui/nifty-core/src/main/java/de/lessvoid/nifty/render/batch/BatchRenderDevice.java:[937,10] de.lessvoid.nifty.render.batch.BatchRenderDevice.FontRenderer is not abstract and does not override abstract method beforeRender(java.lang.Object) in org.jglfont.spi.JGLFontRenderer
[ERROR] nifty-gui/nifty-core/src/main/java/de/lessvoid/nifty/render/batch/BatchRenderDevice.java:[1004,4] method does not override or implement a method from a supertype

Broken at:

- File: https://github.com/void256/nifty-gui/blob/1.4/nifty-core/src/main/java/de/lessvoid/nifty/render/batch/BatchRenderDevice.java

Caused by:

- Commit: void256/jglfont@2f37d869ea80d533cc8d0ebfd0f1737fe4098baf "CustomRenderContext feature added"
- File: https://github.com/void256/jglfont/blob/2f37d869ea80d533cc8d0ebfd0f1737fe4098baf/jglfont-core/src/main/java/org/jglfont/spi/JGLFontRenderer.java
- Line: 66
- Author: @void256 ;-)
Merge pull request #240 from 3xp0n3nt/fix-broken-build

Fix broken build from JGLFontRenderer API change.
fix(jogl): removed getGL2() for some GL calls
fix(jogl): missing shader files added and unused shaders removed (core)
use pgp-maven-plugin instead of gpg-maven-plugin for release signing
README.md added
modified README
Stop the search for droppables in case a element that consumes (is visible to) mouse events is located covering any other droppable
jglfont-core-1.4 added
Merge pull request #241 from mkaring/1.4

Changed search for a droppable
fix: wrong nifty-lwjgl-renderer version
jogamp.version: 2.1.5-01
[maven-release-plugin] prepare release nifty-main-1.4.0
[maven-release-plugin] prepare for next development iteration
Health image example added - you know, like for health bars and stuff

there are probably better ways to do the same but that's what I've come
up with ... anyone care to improve? :)
Add music looping to GdxMusicHandle.