Components callbacks

[artem30801]

About this pull request

Added support of component callbacks!
Rewiews on naming of functions, classes and arguments will be very appreciated, as some of the current method names feel too long or ambigous.

Changes

• Extracted everything not related to function of slash commands from CommandObject to new CallbackObject base class
• Added ComponentCallbackObject and CogComponentCallbackObject to hold component callback data (inherits from CallbackObject)
  • Thus, component callbacks support max_concurency, cooldowns, checks and individual error handlers (same as slash commands do now)
• Added methods to SlashCommand to add, remove and manage component callbacks
  • add_component_callback to registeer function as component callback
    • Support of lists (including empty lists) of message and custom ids
    • custom_id defaults to function name in not specified
  • extend_component_callback to dynamically add combination of message_id and custom_id to existing callback object
  • get_component_callback to get component callback by message_id, custom_id, component_type
  • remove_component_callback to dynamically remove combination of message_id and custom_id from listening for callbacks
  • remove_component_callback_obj to remove all listeners (combinations of message_id and custom_id) assosiated with specified callback object
• Added component_callback decorator to SlashCommand to register function as component callback
• Added cog_component decorator to cog_ext to register cog method as component callback
• Added on_component_callback event triggered along with actual component callback
• Added component callback error handling event on_component_callback_error to work in same manner as slash commands do now

Checklist

• I've checked this pull request runs on Python 3.6.X.
• This fixes something in Issues.
  • Issue:
• This adds something new.
• There is/are breaking change(s).
• (If required) Relevant documentation has been updated/added.
• This is not a code change. (README, docs, etc.)

[LilSpazJoekp]

Just a few suggestions.

[i0bs]

LGTM