Rename JMX MBeans so they are more alligned with other MBeans

• rename the name "bean" to "org.onehippo.hst"
• add a "type" with values "SessionPool" and "SessionPoolCounter"
• add name with values "default", "binaries", "preview",
  "hstconfigreader", "writable"

This will result in:

"org.onehippo.hst:type=SessionPool,name=default"
"org.onehippo.hst:type=SessionPoolCounter,name=default"

instead of:
"bean:name=defaultSessionPool"
"bean:name=defaultSessionPoolCounter"