Merge additional pydocstyle error fixes into development docs

[RNKuhns]

Reference Issues/PRs

This partially addresses docstring updates needed to eventually implement #890.

What does this implement/fix? Explain your changes.

Primarily includes docstring fixes to pass pydocstyle checks that were needed because changes had to be made to some docstrings for numpydoc parsing.

Also includes a couple tweaks to the look of the documentation pages.

• Changes navigation bar titles from users to "user documentation" and developers to "get involved"
• Makes updates to "getting started" page
• Turns on autodoc member ordering by source to order documentation of members (eg. attributes, methods) by the order they show up in source code (not sure this is working)

Does your contribution introduce a new dependency? If yes, which one?

N/A. Just updates docstrings.

What should a reviewer concentrate their feedback on?

Any other comments?

PR checklist

For all contributions

• I've added myself to the list of contributors.
• Optionally, I've updated sktime's CODEOWNERS to receive notifications about future changes to these files.
• I've added unit tests and made sure they pass locally.

For new estimators

• I've added the estimator to the online documentation.
• I've updated the existing example notebooks or provided a new one to showcase how my estimator works.

[RNKuhns]

@mloning can you take a look at the changes in this and merge it into our development documentation branch if they look fine?

Almost exclusively updates to pass pydocstyle checks. Also included minor tweaks to performance metric documentation's .rst file.

[aiwalter]

great work @RNKuhns

[mloning]

Fixed the merge conflicts

[mloning]

Great work @RNKuhns - looks all good to me

[mloning]

this is nice! so we should make sure fit, predict, transform and update are at the top in the code, right?

[fkiraly]

Nice and also fixes docstrings in different places

[mloning]

I've merged this now @RNKuhns - wanted to look at a few other things based on your changes!