Add Sophos logo

[FreeTheTech101]

While migrating from andOTP, I noticed that there was no icon for Sophos. Tested between the text based logo and "S" Shield found on their brand page, and came to the conclusion that the "S" Shield is more recognizable, especially in compact mode. If any changes need to be made before merging, please let me know!

[jamie-mh]

Hi @FreeTheTech101 ,

Thanks for the icon. Looks good!