Colocation cleanup and update dev version number

[lewisblake]

Change Summary

Puts all colocation stuff in a colocation module. Updates the dev version to 0.20.dev0

Related issue number

NA

Checklist

• [x] Start with a draft-PR
• [x] The PR title is a good summary of the changes
• [x] PR is set to AeroTools and a tentative milestone
• [x] Documentation reflects the changes where applicable
• [x] Tests for the changes exist where applicable
• [x] Tests pass locally
• [x] Tests pass on CI
• [x] At least 1 reviewer is selected
• [x] Make PR ready to review

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 79.31%. Comparing base (af621d8) to head (186dbe0). Report is 501 commits behind head on main-dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main-dev #1195 +/- ## ============================================ + Coverage 79.25% 79.31% +0.06% ============================================ Files 129 131 +2 Lines 20220 20229 +9 ============================================ + Hits 16025 16045 +20 + Misses 4195 4184 -11 ``` | [Flag](https://app.codecov.io/gh/metno/pyaerocom/pull/1195/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=metno) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/metno/pyaerocom/pull/1195/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=metno) | `79.31% <100.00%> (+0.06%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=metno#carryforward-flags-in-the-pull-request-comment) to find out more.

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