refs #6317 display instructions before upgrading.

We will by default always run a --dry-run before actually upgrading
and then ask the user for confirmation to execute those updates.
Alternatively a user can use a parameter --yes to avoid asking
for confirmation.
refs #6435 replace possible comma with a dot. Not 100% sure if that works yet
refs #6435 check for floats in a more central place so dimensions do not have to care about this. Makes it a tiny bit slower but less prone to errors
Revert "refs #6317 display instructions before upgrading."

This reverts commit 612b25090f13ee0fde4d4726fc18d08218ea4a74.
refs #6435 make sure we compare values using a dot in getRequestVar
refs #6435 had to patch upgrade.php as serialization is broken when using locale de_DE... should try to submit a pull request forthis otherwise we will not be able to simply update this lib
refs #6435 fix siteCreation fails under circumstances if German locale is used (or any locle using comma instead of dot)
refs #6435 fix evolution filter did cast a float to string resulting in wrong sorting results
refs #6435 fix some more wrong values if a German locale is used

This caused me a lot of headache. I ran the system tests with a German
locale and noticed so many values are completely different. I was looking
for places where there were still any float to string conversions and I
was wondering why the existing fix didn't work until I noticed the
PiwikTracker did not send floats but floats with a comma as decimal
point which in the end was casted to ints etc.
refs #6435 fixed another test in case German locale is used.

This one was not easy to find either. The segment value contained a
comma instead of a dot causing the API to not find anything and to not
return any data.
refs #6435 if a float is assigned to a config value and a german locale is used the wrong value will be saved (5,55 instead of 5.55)
Merge pull request #6610 from piwik/6435

Fix wrong database values when float representation is not set to English standard