Invalid Link and Name for Chart Images

[lucaderi]

In recent ntopng versions there is a new option that allows the chart to be downloaded as image

There are a few issues to fix

• There is a typo in "Downlod"
• The file name should not have spaces or other forbidden chars such as / \, $, " ....
• The URL for downloading the chart offline (e.g. via curl) is not available and it must be implemented

[lucaderi]

The fix is suboptimal because you should replace spaces (or similar charts) with _ or - as zapping space makes rhe filename unreadeable

[uccidibuti]

I replaced all space and '-' with _ and all others special characters with empty char.

[lucaderi]

Verified as fixed