[JENKINS-19990] Support Non-ascii properties

Allows non-ascii characters in "Predefined parameters", "Parameters from properties file" and "For every property file, invoke one build". Encoding can be specified in "Parameters from properties file" and "For every property file, invoke one build".

A new feature in Java 1.6 is used. When running with Java 1.5, this falls back to existing implementation and only ascii characters can be used.

What I do is creating utility class `ParameterizedTriggerUtils`
* readFileToString
** read files with specifying encoding. Existing API `FilePath#readToString` always read files with platform default encoding.
* loadProperties
** load a string as a properties file. It works also works for non-ascii strings in Java 1.6 or later. Also works in Java 1.5, only for ascii string.