Changes reminder fields to have their own form

Reminders submit by button instead of on blur (that was dumb admittedly)
and having their own form now, they will work when js is turned off.

They also hit their own controller when not using ujs, rather than being
a nested item attribute (so their forms are distinctly different.)
Cuts down mass-assignable methods for Item

For item#project_id, uses the project_id in the route rather than
params[item][project_id]. (Nil is okay).

Also, uses build() where appropriate instead of manually assigning
the user_id for an item. Seeds.rb updated appropriately.

Also removes some legacy views.