Plugin SourceWebSVN : Add an option to handle "Multiview" mode in WebSVN.

WebSVN can be configured to use Apache Multivew link format. Theses changes allow user to specify if this option is enabled on not in WebSVN.

Note that theses changes only make the option visible in the WebSVN repos config form. Next step is to check the value of this option so the plugin can format WebSVN links accordingly.

Fix issue #46