refactor managers and handlers.

[stopfstedt]

shedding some weight for the summer. 👙

[homu]

☔ The latest upstream changes (presumably #1399) made this pull request unmergeable. Please resolve the merge conflicts.

[stopfstedt]

recap:

• standardized CRUD-method names in managers, then consolidated them as much as possible into BaseManager and DTOManager.
• refactored handlers to use managers rather than extending them. then consolidated all handers into one class BaseHandler and rewired everything.
• updated all classes that are interfacing with handlers and managers, most notably controllers, voters and commands.
• minor cleanup like code comments corrections and method/class-name case corrections.

[stopfstedt]

140 files less.

~/dev/projects/ilios on master
$ find src -type f | wc -l
991

vs.

~/dev/projects/ilios on refactor_handlers
$ find src -type f | wc -l
848

[jrjohnson]

Holding off on merging until post 3.11

[jrjohnson]

Reviewed as much as possible. Great stuff, lots of less code 💯 this is ready to go once 3.12 is released because I would like to merge it with plenty of time to test.