Configuration Editor: Validate decimal separator for double params

steps to reproduce with the sample app:

1. go to http://localhost:4502/content/contextaware-config-sample/en/config.html

2. add new configuration "Sample Configuration 2"

3. enter a value "123,456" for "Double Param" (using "," as decimal separator, not ".")

expected: a decimal value with "," should not be accepted by the GUI validation, only with ".".
actual: "," is accepted by the GUI, but leads to an error in the backend when saving.

sidenode: tested on windows OS with german language.