Fixes for custom backends

Issue #1224 FIXED - SparkleShare uses <backend> value in plugin, if
present, rather than parsing URL
Issue #1230 FIXED - Added UseSSHKeys and ParseRemoteURL properties
(both true by default) to allow custom backend Fetcher classes to
specify how these elements are handled (if at all - set to false to
make the fetcher class instance responsible for parsing)
Added MarkLogic sparkle repo plugin (uses MLDotNet library)
added gitignore
gi