Patch for building OSGi manifest

Add instructions in build.gradle in order to make OSGi manifest. Next jars should be OSGi compatible.

The plugin used to generate this file is [gradle-bundle-plugin](https://github.com/tomdmitriev/gradle-bundle-plugin)

Here a sample of automatically generated manifest:

```mf
Manifest-Version: 1.0
Bnd-LastModified: 1417794553938
Bundle-ManifestVersion: 2
Bundle-Name: rsyntaxtextarea
Bundle-SymbolicName: rsyntaxtextarea
Bundle-Version: 2.5.4
Created-By: 1.7.0_51 (Oracle Corporation)
Export-Package: org.fife.io;uses:="javax.swing.text";version="2.5.4",org
 .fife.print;uses:="javax.swing.text";version="2.5.4",org.fife.ui.rsynta
 xtextarea;uses:="javax.swing,javax.swing.event,javax.swing.plaf,javax.s
 wing.text,org.fife.ui.rsyntaxtextarea.folding,org.fife.ui.rsyntaxtextar
 ea.parser,org.fife.ui.rsyntaxtextarea.templates,org.fife.ui.rtextarea,o
 rg.fife.util";version="2.5.4",org.fife.ui.rsyntaxtextarea.focusabletip;
 uses:="javax.swing,javax.swing.border,javax.swing.event";version="2.5.4
 ",org.fife.ui.rsyntaxtextarea.folding;uses:="javax.swing.text,org.fife.
 ui.rsyntaxtextarea";version="2.5.4",org.fife.ui.rsyntaxtextarea.modes;u
 ses:="javax.swing.text,org.fife.ui.rsyntaxtextarea";version="2.5.4",org
 .fife.ui.rsyntaxtextarea.parser;uses:="javax.swing.event,org.fife.ui.rs
 yntaxtextarea,org.xml.sax";version="2.5.4",org.fife.ui.rsyntaxtextarea.
 templates;uses:="javax.swing.text,org.fife.ui.rsyntaxtextarea";version=
 "2.5.4",org.fife.ui.rsyntaxtextarea.themes;version="2.5.4",org.fife.ui.
 rtextarea;uses:="javax.swing,javax.swing.border,javax.swing.event,javax
 .swing.plaf,javax.swing.plaf.basic,javax.swing.text,javax.swing.undo,or
 g.fife.ui.rsyntaxtextarea";version="2.5.4",org.fife.util;version="2.5.4
 "
Import-Package: javax.imageio,javax.swing,javax.swing.border,javax.swing
 .event,javax.swing.plaf,javax.swing.plaf.basic,javax.swing.text,javax.s
 wing.text.html,javax.swing.undo,javax.xml.parsers,javax.xml.transform,j
 avax.xml.transform.dom,javax.xml.transform.stream,org.w3c.dom,org.xml.s
 ax,org.xml.sax.helpers
Require-Capability: osgi.ee;filter:="(&(osgi.ee=JavaSE)(version=1.5))"
Tool: Bnd-2.4.0.201411031534
```