refactor Transcriber class

[NickleDave]

Transcriber class is due for a re-factor; should be done in next version

• clean up Transcriber __init__

  • I think currently it's possible to pass in a Meta instance as the argument for config--there's a check in the pre-conditions--but then nothing happens with this, it would just break
  • just drop all this functionality, no-one is using it. Also way too much logic in the __init__ in general
  • could add classmethods if we really want these options, e.g. 'Transcriber.from_config`
  • probably we should just remove the Meta anyway

• more broadly what does Transcriber do?

  • provide a convenient way to do from_file and to_annot for all annotation formats,
    without needing to work with the functions (and soon, classes) directly
  • the "right" way to do this would be to pass in the functions themselves as arguments,
    and have a classmethod Transcriber.from_format('simple-seq') (I don't love the method name from_format)

class Transcriber:
    def __init__(from_file, to_annot):
         self.from_file = from_file
         self.to_annot = to_annot

    @classmethod
    def from_format(format):
        ...

    @classmethod
    def from_config(config):
        ...

[NickleDave]

• the "right" way to do this would be to pass in the functions themselves as arguments,
  and have a classmethod Transcriber.from_format('simple-seq') (I don't love the method name from_format)

ended up doing basically this.
Transcriber.from_format('simple-seq'), for example, returns an instance of a SimpleSeq, already instantiated, using its from_file method. Methods like to_annot can then be called on this returned instance, instead of Transcriber having to handle them or even know they exist