add OSGI support for server side gwtp libraries

This is proposal for OSGi-fication of GWTP server side libraries. 
It needs to be tested. Actually, I don't know which API should be exported and which are private.
There is also one OSGi like dirty thing in gwtp. Modules gwtp-dispatch-common-shared and gwtp-dispatch-rpc-shared exports same package (com.gwtplatform.dispatch.shared) whis is not good, but it works using split OSGi features. I tested it on karaf 3.0.1

Example of karaf feature.xml:
```xml
<?xml version="1.0" encoding="UTF-8"?>
<features name="karaf-features-1.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xmlns="http://karaf.apache.org/xmlns/features/v1.0.0"
          xsi:schemaLocation="http://karaf.apache.org/xmlns/features/v1.0.0 http://karaf.apache.org/xmlns/features/v1.0.0">
    <feature name="gwt-server" version="2.6.1">
        <!--<bundle>wrap:mvn:javax.validation/validation-api/1.0.0.GA</bundle>-->
        <bundle>wrap:mvn:com.google.gwt/gwt-servlet/2.6.1</bundle>
        <bundle>mvn:com.google.inject/guice/3.0</bundle><!-- https://code.google.com/p/google-guice/wiki/OSGi gwtp -->
        <bundle>mvn:com.google.inject.extensions/guice-servlet/3.0</bundle>
        <bundle>mvn:com.google.inject.extensions/guice-assistedinject/3.0</bundle>
        <bundle>mvn:javax.inject/com.springsource.javax.inject/1.0.0</bundle>
        <bundle>mvn:org.apache.servicemix.bundles/org.apache.servicemix.bundles.aopalliance/1.0_6</bundle>
    </feature>
    <feature name="gwtp-server" version="1.3">
        <feature version="2.6.1">gwt-server</feature>
        <bundle>mvn:com.gwtplatform/gwtp-dispatch-rpc-server/1.3-SNAPSHOT</bundle>
        <bundle>mvn:com.gwtplatform/gwtp-dispatch-rpc-server-guice/1.3-SNAPSHOT</bundle>
        <bundle>mvn:com.gwtplatform/gwtp-dispatch-rpc-shared/1.3-SNAPSHOT</bundle>
        <bundle>mvn:com.gwtplatform/gwtp-dispatch-common-shared/1.3-SNAPSHOT</bundle>
        <bundle>mvn:com.gwtplatform/gwtp-mvp-shared/1.3-SNAPSHOT</bundle>
    </feature>
</features>
```