Batch loading

[Iaxama]

This PR adds the possibility to load large ROS bags datasets without filling your RAM completely.
To achieve that the bag is read in its entirety but only the info about a certain chunk of data is retrieved. These infos contain the start and end timestamp of the data contained in that chunk and the position in the file where the chunk can be read. The data can therefore be read on request providing the desired time range. All the data outside that time range can be offloaded from RAM for retrieving it later. This can be done through the DataProvider class which needs to be initialized with the proper function to load the data. In fact that class only provides an interface for any module that needs to retrieve data on request, in order to allow extension of current implementation to formats other than ROS bags.

Being a major change further testing is recommended before merging.