Improve the usability in OSGi environment

* Align the value of __Bundle-RequiredExecutionEnvironment__ with the specification  http://wiki.osgi.org/wiki/Execution_Environment
* Maven bundle plugin has default value of __<_removeheaders>__ if it's explicitly defined its value overwritten, I added the default value to make better looking the generated MANIFEST.MF

* Maven bundle plugin has these default values:
```xml
<Bundle-Name>${project.name}</Bundle-Name>
<Bundle-SymbolicName>${project.groupId}.${project.artifactId}</Bundle-SymbolicName>
<Bundle-Description>${project.description}</Bundle-Description>
<Bundle-Version>${project.version}</Bundle-Version>
<Bundle-DocURL>${project.url}</Bundle-DocURL>
```

* Blueprint, Pipes and Gremlin fails in OSGi because OrientDB modules does not import the necessary packages. I tested the http://code.google.com/p/orient/wiki/GraphEdTutorial tutorial in OSGi and it works with this fix.