More accurate annotations on task properties
#7 - Change pitest task type to JavaExec

This allows to launch PIT with custom classpath containing the PIT version
defined by the user using pitestVersion parameter.
PIT is no longer a compile time dependency of the plugin
Change configuration parameters types to less error prone

jvmArgs from String to List<String> and timeoutFactor from String to BigDecimal
Update documentation
Upgrade wrapper to 1.11
Merge branch 'topic/i7-javaexec'