Allow the user to load specific channels

[vedran-kasalica]

Current loading of the data depends on the filenames, however that is not fixed. We should look into allowing users to specify channels that they are interested in instead of naming explicit file_names.

For example, in the PPP section of this script naming of the binary files is assumed:

• metadata json file name ends with "_meta.json"
• time bin file_name ends with "_time.bin"
• IMU data bin file_name ends with "_samples.bin"