Option to send observation in text message (SMS) without photo

[gmaclennan]

Currently the "Share" option for an observation includes any photos. If the user chooses to share via a text (SMS) message and the observation has any photos attached, then these photos are included in the text message. Sending a photo via text message causes it to be sent as MMS (Multimedia Message Service) which for many users has an additional cost and is not included in free text plans. For users without credit the result is the message will just not send. With lockdown measures in various countries and restricted travel it is particularly important for Mapeo users to be able to send messages via SMS for urgent issues.

We need a way for users to share an observation via SMS without photos. This could be an option on the share sheet, although it might require us to implement a custom share sheet as opposed to the default that we currently use. Related, see #380