Plugin dependency visualization utility

Issue: http://issues.qcadoo.org/browse/QCADOO-115

Brief

Create a simple JavaScript/HTML utility that analyses multiple qcadoo-plugin.xml descriptors and returns a graph showing their dependencies.

Visualization component: http://code.google.com/p/canviz/

Demo:http://www.ryandesign.com/canviz/

Use the dot layout engine.

qcadoo-plugin.xml files should be downloaded for the analysis. There should be a derscriptors.xml files in which we have a list of descriptor locations.

Example

Descriptors list
<descriptors>
  <group name="MES - open source" level="2">   
    <archive url="https://github.com/qcadoo/mes/zipball/master" />
    <descriptor url="https://raw.github.com/qcadoo/qcadoo-incubator/master/warehouse/src/main/resources/qcadoo-plugin.xml" />
    <!-- more descriptors -->
  </group>
  <group name="framework" level="1">
    <archive url="https://github.com/qcadoo/qcadoo/zipball/master" />
    <!-- more descriptors -->
  </group>
</descriptors>