Measurement logging: parametrization

[MatthieuDartiailh]

To allow the parametrization of the measurement logging hook, a new dedicated plugin (similar to the TextMonitorPlugin) should be created. This plugin would accept LogEntries contributions that would be responsible for analyzing a Measurement and reporting the required information. The execution hook would hold a list of such LogEntries and execute them sequentially.

Since editing the entries on a per measurement basis would make little sense, the LogEntries and their parameters should be stored in the plugin preferences. Their edition hence requires to complete the edition of the application preferences. In this particular case, providing a custom edition page would be more meaningful than attempting to rely on an automatic GUI generation.