Allow for multiple url prefixes and suffixes in HelpUtil

com.atlassian.jira.web.util.HelpUtil parses files like help-paths.properties, and provides convenience methods for building links from that data. Each link is put together by combining a path fragment with a prefix and suffix. The utility class allows for exactly one prefix+suffix pair. This means we can't use it in Studio, because we need to point users to entirely different sites depending on whether they are in Studio mode vs JIRA Standalone mode.

Would it be possible to make this more flexible? I think a simple solution could be to make defaultHelpPath and helpPaths instance fields rather than static, so that multiple instances of HelpUtil can be created for different .properties files (I can't see why those fields need to be static).