- As todos are created/updated inside the TodoService
we repopulate the cache just there for both pending/done todos
- Todos as mark as done from the TodosController we update cache
there too
- All the added methods are kept in the User class for cohesion

This reverts commit 13e37a3e.

Added a button into the sidebar for issues & merge requests to allow users to manually create todo items

Closes #15045

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

When a build fails for a commit, create a todo for the author of the
merge request that commit is the HEAD of. If the commit isn't the HEAD
commit of any MR, don't do anything. If there already is a todo for that
user and MR, don't do anything.

Current limitations:
- This isn't configurable by project.
- The author of a merge request might not be the person who pushed the
  breaking commit.

Signed-off-by: NRémy Coutable <remy@rymai.me>

Since potentially the previous assign-task has already been handled.