Split package view code modules to smaller files

[MythicManiac]

Split the package related Django views code classes to multiple smaller files, roughly one per view class or grouped by the same functionality.

This commit does not include any functionality changes outside of changes to import locations.

[codecov[bot]]

Codecov Report

Attention: 42 lines in your changes are missing coverage. Please review.

Comparison is base (f3d8e4c) 93.03% compared to head (3837c3f) 93.05%.

Files	Patch %	Lines
...ango/thunderstore/repository/views/package/list.py	86.51%	23 Missing and 6 partials :warning:
...go/thunderstore/repository/views/package/detail.py	94.50%	2 Missing and 3 partials :warning:
...go/thunderstore/repository/views/package/create.py	92.00%	4 Missing :warning:
...go/thunderstore/repository/views/package/_utils.py	88.88%	1 Missing and 1 partial :warning:
django/thunderstore/repository/views/repository.py	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #991 +/- ## ========================================== + Coverage 93.03% 93.05% +0.01% ========================================== Files 298 305 +7 Lines 8705 8750 +45 Branches 777 777 ========================================== + Hits 8099 8142 +43 - Misses 500 502 +2 Partials 106 106 ```

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