the swicth because order is not important for these.

ModuleList serves as a container for VariableGroups. The VariableGroups
mirror xml modules in the config file.

Xml parsing logic factored out to class ConfigParser.

Unfortunatly this currently breaks the ServerHistory module, as it relies on slashes in accessor names. The MicroDAQ module had the same issue but has already been fixed. This fix can be adopted to the ServerHistory module as well.

Now one can add ScalarOutput and ArrayOutput variables to the history modules by using tags.

This is still not nice. Now for every data type an individual module needs to be created.

Do not rely on EntityOwner for accessig Application object.

- renamed timeout to period.
- introduced PeriodicTrigger::sendTrigger
- mainloop logic bypassed on startup if owner application is in testable
  mode.

- Timeout is now in milliseconds to allow more flexibility
- Default timout can be specified in the constructor
- Make sure the time interval is perfectly matched by using sleep_until instead of sleep_for

- Make data decimation configurable
- Addded some documentation
- Some code cleaning (eliminate warnings, move internal classes into detail namespace)

If sendMessage is used before chimeraTK process variables are initialized an internal buffer is used to store those
messages. Once the process variables are initialized the messages from the buffer are send.

Include descriptions of the owning Module in the descriptions of each process variable to make them more complete.