Flatten module hierarchy through re-exports

Can we make the module hierarchy more flat via re-exports? Imports are quite tedious already.

Should get :noindex: for the re-exported modules for sphinx to avoid WARNING: more than one target found for cross-reference.

Suggestion

• finam
  • From core.interfaces
    • FinamLogError, ... (all errors)
    • ComponentStatus
    • Loggable
    • NoBranchAdapter
    • (all the interfaces like IComponent are normally not required by devs, so should stay in core.interfaces)
  • From core.sdk (everything except IOList and IOType)
    • AAdapter
    • AComponent
    • ATimeComponent
    • Input
    • CallbackInput
    • Output
  • From core.schedule
    • Composition
  • From data and sub-modules
    • FinamDataError
    • Info
    • CellType
    • Location
    • NoGrid
    • UniformGrid and all other non-abstract grids
    • Not sure about functions like to_xarray, get_data, etc. Maybe have them under finam.data?
• finam.data
  • canonical_data()
  • all the functions from finam.data.tools?