Adopt a plugin structure

[markstory]

Move the application code into 3 plugins for the various surfaces in docket.

• Feeds - contains the feedreader
• Tasks - contains projects and todos
• Calendar - contains the calendar integration for tasks and google endpoints

Each plugin contains its own API endpoints as well as the htmx endpoints. Layouts and fixtures are still in the application, but I'll fix that up next.

[codecov]

Codecov Report

Attention: Patch coverage is 1.44928% with 68 lines in your changes missing coverage. Please review.

Project coverage is 51.76%. Comparing base (73965d4) to head (e00541d).
Report is 27 commits behind head on master.

Files with missing lines	Patch %	Lines
plugins/Calendar/src/Service/CalendarService.php	0.00%	8 Missing ⚠️
...s/Feeds/src/Model/Table/FeedSubscriptionsTable.php	0.00%	8 Missing ⚠️
plugins/Tasks/src/Model/Table/TasksTable.php	0.00%	4 Missing ⚠️
...ns/Calendar/src/Model/Table/CalendarItemsTable.php	0.00%	3 Missing ⚠️
.../Calendar/src/Model/Table/CalendarSourcesTable.php	0.00%	3 Missing ⚠️
...eds/src/Controller/FeedSubscriptionsController.php	0.00%	3 Missing ⚠️
plugins/Tasks/src/Model/Table/ProjectsTable.php	0.00%	3 Missing ⚠️
plugins/Calendar/src/CalendarPlugin.php	0.00%	2 Missing ⚠️
plugins/Feeds/src/FeedsPlugin.php	0.00%	2 Missing ⚠️
plugins/Feeds/src/Model/Table/FeedItemsTable.php	0.00%	2 Missing ⚠️
... and 23 more

Additional details and impacted files

@@              Coverage Diff              @@
##             master      #60       +/-   ##
=============================================
- Coverage     92.04%   51.76%   -40.29%     
- Complexity      864      866        +2     
=============================================
  Files           170      172        +2     
  Lines          8602     8636       +34     
=============================================
- Hits           7918     4470     -3448     
- Misses          684     4166     +3482     

Flag	Coverage Δ
flutter	90.60% <ø> (+0.05%)	⬆️
phpunit	18.40% <1.44%> (-74.95%)	⬇️

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