A compose screen built for focused writing

We moved the compose preview to the right so you can see how your post will look as you type. The character count now appears as a circular meter like on X, and the 140-character limit for free accounts is checked the same way X counts it (for example, a Japanese character counts as 1 and a letter or digit as 0.5). We also tidied up the toolbar, how threads start, and the order of the save and schedule buttons.