Review content of metadata in detector config files

[ascillitoe]

Our detector self.meta attribute currently contains the following information:

DEFAULT_META = {
    "name": None,
    "online": None,  # true or false
    "data_type": None,  # tabular, image or time-series
    "version": None,
    "detector_type": None  # drift, outlier or adversarial
}  # type: Dict

Whereas the metadata in detector config files contains:

[meta]
version = "0.10.0rc1"
config_spec = "0.1"
version_warning = false

We should review what content it makes sense to include in detector config files. Fields such as detector_type and online could be useful to view without instantiating a detector. In #564 it was decided not to include the entirety of self.meta in config files since this leads to excessive duplication (e.g. name, backend and data_type).

[ascillitoe]

We should also review the intention behind the data_type kwarg, and whether it is even needed.