Core: restructure underlying data structure

[skim0119]

Description

• Relocate Data and DataManager module into miv.io.openephys.
• Add miv.io.asdf to support ASDF type files. ASDF file conversion to spiketrain #77
• Relocate data types in miv.core into miv.core.datatype
• Fix documentation and test accordingly.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• make test
• New tests implementation

Checklist:

• My code follows the style guidelines of this project.
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings/errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been addressed and published in downstream modules
• There are no other PR/Issues that is blocking this PR.