Improvement of the REST service:
* add the possibility to get the step logs for a build

e.g. {{http://localhost:8810/rest/builds/14/logs}} returns
{code}
<xml>
<Steps>
<Step>
  <name>root</name>
  <node>localhost</node>
  <log>
    <logEntry>
      <date>2012-09-02T18:01:34.000+02:00</date>
      <logLevel>INFO</logLevel>
      <message>...</message>
    </logEntry
    <logEntry>
[..]
    </logEntry>
  </log>
</Step>
</Steps>
{code}
XML structure loosely oriented on the BuildLogEntry class

* and the possibility to just get the log of one certain step:
e.g. {{http://localhost:8810/rest/builds/14/logs?stepPath=root}} returns
{code}
<Step>
  <name>root</name>
  <node>localhost</node>
  <log>
    <logEntry>
      <date>2012-09-02T18:01:34.000+02:00</date>
      <logLevel>INFO</logLevel>
      <message>...</message>
    </logEntry
    <logEntry>
[..]
    </logEntry>
  </log>
</Step>
{code}