Support Windows paths in Maven properties

- When passing custom configuration or logs location to Maven,
  use "/" inside property, so we can override it with window's
  path separators "\".

  Any custom value must have ending separator, either "/" for
  Linux or "\" for Windows

  Apply to ${perun.conf}, ${perun.conf.custom} and ${perun.log} properties.

- All found references in pom.xml, app-context.xml and properties files updated
  to respect new scheme.

When merged, check Jenkins builds if they provide proper value for customized builds.