Add support for variables, "+" and "#"

[NiklasCi]

This PR adds support for

• variable support via overwriting the applyTemplateVariable function of the class DataSource.
  • Now topics can contain variables. E.g.: tlm/${Device}/measurement
  • Single selection and all selection for repeating panels works
• + operator of mqtt
  • e.g. tlm/+/measurement or tlm/+/measurement/+
• # operator of mqtt
  • e.g. tlm/device1/#