blf FIle Metadata

### Is your feature request related to a problem? Please describe.
When using the `BLFReader()`, file metadata is scarce (file, object_count, sizes, timestamps). Some other information would be very interesting, like applications that created the file and especially the channel list and channel types.

### Describe the solution you'd like
Add more metadata to the blf object, namely application name and especially channel information. This should be in the file metadata since other software (namely MATLAB) produces fairly detailed data on channels before loading actual data, like
```
ChannelID Protocol Objects
_________ ________ _______

1 "CAN" 0
2 "CAN FD" 6048410
3 "CAN" 5782778
4 "CAN FD" 0
```

This can really help parsing the file. Alternatives see below

### Describe alternatives you've considered
When running through the message genarator, messages contain the channel attribute. This is just an `int` value which suffices to sort the messages but has no informations as shown above.