Show explanation of observations synced from another user

[gmaclennan]

We show observations synced from other devices (as opposed to observations recorded on the current device) with a blue lightning mark in the top-right. It is not possible to edit observations synced from other devices. This is not obvious for the user - it's not clear what the blue lightening means or why they cannot edit the observation.

We need some way of showing the user what the blue lightning mark means and why they cannot edit the point. One option is to make the blue lightning icon a button that shows a modal with an explanation.