Add ability to compose an email

[msp301]

Before I can consider using Pinbox, I need to be able to create a new email.

• Clicking on the '+' FAB icon should open an email editor
• Email editor should allow me to set recipient address(es)
• I can send email to the 'pinbox-server' back-end to handle the actual email sending

[msp301]

Have started fleshing out the UI for composing emails by including Quill editor.

I think it makes sense for the editor to always be in a right-hand side pane on desktop so that you are able to browse emails at the same time as writing one for referencing things. On mobile we should just show the editor in full screen due to lack of space.

Unsure how to keep a split view for desktop view whilst using a single pane view for mobile.