Add ability to periodically check RRDfiles for errors in batch

[xmacan]

Tested by @bmfmancini , thank you

[TheWitness]

Very good work @xmacan. I'm impressed. The one PSR comment I would like to make is that you should remove the empty lines after the following loop/logic constructs:

while
if/then/else
do
switch

I'm normally doing this:

$something = something _else;
// Always line here
if (something) {
    // No extra lines here
    so_something();
    // No extra lines here
}
// Always extra line here

I hope you get the picture. If you can do those corrections, I think it's ready to merge. Changelog? I feel silly asking :)

[TheWitness]

1. CHANGELOG
2. Remove extra whitespace as articulated in my first comment.

Great work!

Looks good now