I know. They hate the term. But it is impossible to talk about Mark and Jay Duplass (as writers, anyway, aside from their work as actors, directors, and producers) without the dreaded term “mumblecore,” which was applied to their early microbudget work because of the improvisational, shaggy-dog, millennial-ness of their work. Traces of that remain in “Table 19,” cross-bred with a more conventional romantic comedy, and it turns out to be a welcome blend of sweet and sour. This is not the usual Jennifer/Jessica with a quippy best friend, a meet cute, and a makeover.