New composer is difficult to use with one hand

Noting some feedback from @AmandineLP that she's finding the new composer difficult to use with one hand— reachability to the (+) icon on the left is tough on an iPhone X.

One suggestion from looking at other apps is we could consider having some 'shortcut' buttons placed within easier reach for the most common actions; e.g. for sending photos.

@gaelledel @gileluard given commitments/things in flight, when do you think would be the best time for us to discuss this in more detail? I think it'd be good to have an initial 60min chat, the things on my mind are:

- Potential long term directions
- Potential quick wins for the immediate term
- If there's any simple prototyping we want to do
- If there's a simple way we can facilitate 'hallway' testing on device while in pandemic

...before we make any specific commitments.