Form: Serverside validation rules

[Hackwar]

[HLeithner]

Backport notice regex has been merged into 5.1 Missing new feature entry in 5.1

Regex information incomplete, seems 2 attributes are needed (didn't checked the comments why this is needed because normal regex allows to add them at the end between controller character) and is not documented

is this true for other rules too? didn't looked at them.

[HLeithner]

@Hackwar can you please fix this, so it's ready for 5.1 release