Option to edit all recurrences of a shift

[adambray]

I think it would be really cool if when I go to edit a shift, and the
shift was applied as part of a template, that it should offer to let me
edit the template and all other shifts already applied as part of that
template.

That is, so if Sally decides that her Tues 5-10 shift is too long, I can
shorten all of them to 5-8 at once.

I know this one could be tricky, but I'd like to get it down for maybe
this summer while I'm thinking about it.