Make log message in invalid regular expressions more verbose

Make logging of erratic regular expressions more verbose to help
identification and resolving of the configuration issue:

eg.:
old: 24 Dec 18:40:09 - [error] [change:Strip kW] Invalid regex: *kW
new: 24 Dec 18:40:09 - [error] [change:Strip kW] Invalid regular
expression: /*kW/: Nothing to repeat

old: 24 Dec 20:15:57 - [error] [change:Strip kW] Invalid regex: *kW
new: 24 Dec 20:15:57 - [error] [change:Strip kW] Invalid regular
expression: /[kW/: Unterminated character class
Add validation to Change node editor for invalid regex

This change adds input validation to the gui of Change Nodes to prevent
the user from unintentionally entering an invalid regular expression
(in case the ‘use regular expressions’  option is enabled).

The user will be notified (using the RED notification mechanism) on the
specific error code to help resolve the issue.