Logfile fixes part2

[frenchie71]

Adding automatic maintenance options to the config json
Adding a Downoad Button for logfiles
Adding Maintenance functions rollover, split, delete, view for logfiles
Adding Log File Maintenance Section for FileList on SPIFFS to the UI

[frenchie71]

should fix most of #285 - automatic functions need to be implemented still

[omersiar]

Great implementation, this was the original plan. Nicely done. 👍

[frenchie71]

Thank you - there are a handful of caveats though at the moment

• Split is blocking, i.e. there is no User Interface Update on the progress but it does not trigger the watchdog - and it is reasonably fast (roughly 10 sec for a 100K logfile)

• Corrupt logfiles will not load correctly. This is caused by at least three things:

• the JSON.parse in the esprfid.js throws an error if it can't convert

• the ws.textAll in log.esp throws an error if there are garbage characters - the client will wait eternally for the next page

• the SPIFFS readStringUntil is blocking and does not stop if it reads upon EOF. This will definitely trigger the watchdog and reset the unit

I might work on these in the next couple of days or weeks ;-)