Userland list of files to exclude from integrity check and updates #3419

As from changeset 1957 it would be useful for piwik admin to configure a list of files to be excluded from integrity check and preserved on updates.

I'm thinking, for example, to the logos, css and templates in the default theme that one, as no themes support is still available in piwik, has to customize to have his own customized theme ..

nowadays I'm forced to remove integrity checksums entries in

config/manifest.inc.php

to avoid piwik warning ...

BTW, in cs 1957 the file "robots.txt" is hardcoded in two different fils .. not so good .. a globalized exclude list should be present in a single place

If you see the warnings and expect them, it's OK, just ignore them. Design decision to view all file changes.