Add Composer to each timeline

[DeadSuperHero]

Adding this will probably require some refactoring, but it would be nice for users to be able to post a status from any timeline that they are viewing. This is an expected behavior for platforms such as Diaspora, where one can post from their own profile, their personal timeline, a tag search timeline, or from a public timeline.

At the moment, only src/components/home.vue calls the Composer element. I played around with this a bit, and it looks like it's not currently possible to call said component directly from the Timeline itself, without incorporating some of the methods currently being leveraged by home.vue.