Standardise input files as argument to `run_tracker`

[sjavis]

Currently input files are specified in the parameter classes for the trackers. This are a number of issues related to this:

• There is no standardisation across trackers.
• They must be defined in the parameter classes. This will make it difficult to define default parameter sets (Create default parameter sets #175).
• Trackers often check that the file exists when they are instantiated.
  • This complicates testing as they must be created or mocked.
  • It has prevented instantiating the tracker objects in load_tracker_metadata.
• It puts somewhat useless data in the output metadata (it should be superseded by actually propagating the metadata from the input files)
• It makes concatenating the output files in batching more complicated.

The input files are also not really relevant to the configuration of the tracking algorithms, so I propose instead passing them as an argument to run_tracker (and other appropriate functions such as detect). By standardising this it will allow the input files to more easily be passed in the batching.

This is a relatively significant change to the core UI so I would suggest the next release version to be 1.0 to align with semantic versioning.