For each filesystem interaction be more specific if we want to read from
the file or write to it.

Doing a non-creating read on the loading of the settings file, otherwise
an empty file could be created, and when reading that empty file for the
initial settings I would expect an error (or random data) when reading.

Apply a few changes that were requested in the PR during the review.

# Conflicts:
#	src/CMakeLists.txt
#	src/displayapp/Apps.h
#	src/displayapp/DisplayApp.cpp
#	src/displayapp/Messages.h
#	src/displayapp/screens/settings/Settings.cpp