When opening a page such as /web/timelines/home in a desktop browser, the
cursor was automatically placed in the textarea of the compose form.
When using the keyboard for navigation (using a browser plugin like vimium or
vim vixen, or just to hit 'space' to scroll down a page), you have remember to
leave the field before using that.
Since you only visit the page to write a new post some of the time, this PR
attempts to have nothing focused initially (and require the user to click or
e.g. use 'tab' to focus the textarea).
Tested:
* /web/timeslines/home no longer autofocuses the compose box
* pressing the 'n' hotkey still focuses the compose box
* clicking 'reply' for a post still focuses the compose box
* replying to a CW'ed post still focuses the compose box
* introducing the CW field still focuses the CW field
* introducing the CW field for a reply still focuses the CW field
* removing the CW field still focuses the compose box
* /web/statuses/new still autofocuses the compose box
fixes#15862