Improve admin view of log files

[batopa]

Related #301 there are some improvements to implement for file log view in Administration module.

• move "..." on top of log entry
• add refresh button for each file
• add button to enable/disable an ajax autoupdate for each file
• highlight the rows with errors intercepting Exception string
• list of all files present in logs directory. Now are listed only debug.log and error.log but other log files can be generated from utility page in admin module or from some shell script

[didoda]

commit fe2c49b
done first 3 points of list and 5th:

move '...'
refresh button
autoupdate check
...
list of all files present in logs dir

[batopa]

"Refresh file" and "autoupdate" actions should show a loader while data is fetched.
The .loader css class can be used.
The div that contains logs should be emptied and loader class added to it (use show() too because loader has display: none;).
When data are loaded remove loader class.