fix(*): make templates work with custom interpolation symbols

Previously, components specifying their own templates (such as Dialog, Toast etc) assumed that the
interpolation start-/endSymbols where `{{` and `}}`, thus breaking in apps using custom symbols.
This commit introduces a new `$mdUtil` method for replacing the "assumed" symbols (`{{`/`}}`) with
the actual ones.

Closes #877
@ajoslin: Right now there are any components that need this replacing other than dialog and toast (both interimElements), so moving the `replace` here would work as well. I put it into `$mdUtil` in case it might be needed by non-interim elements, but right now it isn't necessary. So, I'll move it here I guess.

@ThomasBurleson: Note, that only "manually" compiled elements have this issue. If you use `{{...}}` in a directive's template (as is the case for `mdTextFloat`), Angular itself will denormalize the templates when compiling.