[MODCLUSTER-209] Added ability to to output text/xml for DUMP and INFO

Added ability to to output **_text/xml_** for **DUMP** and **INFO** commands in addition to previous text/plain.

default is still **_text/plain_** and browser by default is still going to output text/plain.

#### sample **INFO** output:

````bash
$ curl -X INFO http://127.0.0.1:6666 -H "Accept: text/xml" | xmllint --format -
````
````xml
<?xml version="1.0" standalone="yes"?>
<Info>
  <Nodes>
    <Node id="1" name="MyClusterB">
      <Balancer>mycluster</Balancer>
      <LBGroup>mycluster</LBGroup>
      <Host>127.0.0.1</Host>
      <Port>4445</Port>
      <Type>http</Type>
      <Flushpackets>Off</Flushpackets>
      <Flushwait>1</Flushwait>
      <Ping>10</Ping>
      <Smax>0</Smax>
      <Ttl>60</Ttl>
      <Elected>0</Elected>
      <Read>0</Read>
      <Transfered>0</Transfered>
      <Connected>0</Connected>
      <Load>99</Load>
    </Node>
    <Node id="2" name="MyCluster">
      <Balancer>mycluster</Balancer>
      <LBGroup>mycluster</LBGroup>
      <Host>127.0.0.1</Host>
      <Port>4444</Port>
      <Type>http</Type>
      <Flushpackets>Off</Flushpackets>
      <Flushwait>1</Flushwait>
      <Ping>10</Ping>
      <Smax>0</Smax>
      <Ttl>60</Ttl>
      <Elected>0</Elected>
      <Read>0</Read>
      <Transfered>0</Transfered>
      <Connected>0</Connected>
      <Load>99</Load>
    </Node>
  </Nodes>
  <Vhosts>
    <Vhost id="1" alias="mycluter">
      <Node id="1"/>
    </Vhost>
    <Vhost id="1" alias="mycluter">
      <Node id="2"/>
    </Vhost>
  </Vhosts>
  <Contexts>
    <Context id="1">
      <Status id="1">ENABLED</Status>
      <Context>/cluster</Context>
      <Node id="1"/>
      <Vhost id="1"/>
    </Context>
    <Context id="2">
      <Status id="1">ENABLED</Status>
      <Context>/clusterA</Context>
      <Node id="2"/>
      <Vhost id="1"/>
    </Context>
    <Context id="3">
      <Status id="1">ENABLED</Status>
      <Context>/clusterB</Context>
      <Node id="2"/>
      <Vhost id="1"/>
    </Context>
  </Contexts>
</Info>
````
#### sample DUMP output:

````bash
$ curl -X DUMP http://127.0.0.1:6666 -H "Accept: text/xml" | xmllint --format -
````
````xml
<?xml version="1.0" standalone="yes"?>
<Dump>
  <Balancers>
    <Balancer id="1" name="mycluster">
      <StickySession>
        <Enabled>1</Enabled>
        <Cookie>JSESSIONID</Cookie>
        <Path>jsessionid</Path>
        <Remove>0</Remove>
        <Force>1</Force>
      </StickySession>
      <Timeout>0</Timeout>
      <MaxAttempts>1</MaxAttempts>
    </Balancer>
  </Balancers>
  <Nodes>
    <Node id="1">
      <Balancer>mycluster</Balancer>
      <JVMRoute>MyClusterB</JVMRoute>
      <LBGroup>mycluster</LBGroup>
      <Host>127.0.0.1</Host>
      <Port>4445</Port>
      <Type>http</Type>
      <FlushPackets>0</FlushPackets>
      <FlushWait>1</FlushWait>
      <Ping>10</Ping>
      <Smax>0</Smax>
      <Ttl>60</Ttl>
      <Timeout>0</Timeout>
    </Node>
    <Node id="2">
      <Balancer>mycluster</Balancer>
      <JVMRoute>MyCluster</JVMRoute>
      <LBGroup>mycluster</LBGroup>
      <Host>127.0.0.1</Host>
      <Port>4444</Port>
      <Type>http</Type>
      <FlushPackets>0</FlushPackets>
      <FlushWait>1</FlushWait>
      <Ping>10</Ping>
      <Smax>0</Smax>
      <Ttl>60</Ttl>
      <Timeout>0</Timeout>
    </Node>
  </Nodes>
  <Hosts>
    <Host id="1" alias="mycluter">
      <Vhost>1</Vhost>
      <Node>1</Node>
    </Host>
    <Host id="2" alias="mycluter">
      <Vhost>1</Vhost>
      <Node>2</Node>
    </Host>
  </Hosts>
  <Contexts>
    <Context id="1" path="/cluster">
      <Vhost>1</Vhost>
      <Node>1</Node>
      <Status id="1">ENABLED</Status>
    </Context>
    <Context id="2" path="/clusterA">
      <Vhost>1</Vhost>
      <Node>2</Node>
      <Status id="1">ENABLED</Status>
    </Context>
    <Context id="3" path="/clusterB">
      <Vhost>1</Vhost>
      <Node>2</Node>
      <Status id="1">ENABLED</Status>
    </Context>
  </Contexts>
</Dump>
````

representation of output is almost a map to existing **_text/plain_**.