Central Deprecation Proposals Issue

[hoxbro]

As we now have access to sub-issues, this is a good way to have a central issue for discussion. The name next to a proposal will be assigned to create a sub-issue, and when that is created, I will replace it with the issue number.

Effort level: Big

1. Remove IPython magic (@hoxbro)
2. .options method (duplicative of .opts) (@jlstevens)
3. Limit .to API to only be available for Dataset (@hoxbro)

Effort level: Medium

1. Scrubber (@jlstevens)
2. color_index and family (@hoxbro)
   a. Check if it warns
   b. If it warns, we could likely remove it in the next minor; otherwise, we should make it warn in the next patch version.
3. Remove automatic rc-file (@hoxbro)
   a. Replace it with hv.extensions(rc_file="~/.holoviewsrc")

Effort level: Small

1. Remove unused configs future_deprecations and warn_options_call
2. Remove dash support

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These deprecations points were made in collaboration with @jlstevens and @Azaya89