Update path logic

[RRosio]

Correcting the handling config provided path to be inline with fsspec

• verify fix
• update tests
• update frontend calls
• update path parsing for tree building

[RRosio]

PR Notes:

• client and tests by Martin
  • additional non-browser client header X-JFS-Client to address missing xsrf cookie errors
• updates to filesystem path using the filesystem name, allowing a prefix path for only local and memory filesystems
  • assuming local filesystem root is server root
• updates to api tests to account for path updates and new handlers
• new file content handlers accepting binary data
• updates to the frontend user paths displayed and copied
• updates to ui-tests