[ENHANCEMENT] Additions to checkAllsky.sh

[EricClaeys]

Since quite a few people have problems with missing, corrupted, and/or incorrect entries in Module and Overlay files, I suggest adding checks to checkAllsky.sh to find these problems.
We can start off small (looking for problems people have already identified), and as new problems arise, add checks for those as well.

checkAllsky.sh should probably be run automatically once a week (?) if the settings file was updated in the last week.
This will catch problems from # 1 as well as any new problems that appeared.