Support VFS methods with no argument

[mahsashadi]

Hi @andersevenrud
Due to this comment, imagine we have capabilities method with no argument in client-sie:
method call:

vfs.capabilities();

osjs-client/src/vfs.js

export const capabilities = (adapter, mount) => () => {
  const cached = capabilityCache[mount.name];
  if (cached) {
    return Promise.resolve(cached);
  }
  return adapter.capabilities(mount)
    .then(capabilities => {
      capabilityCache[mount.name] = capabilities;
      return capabilities;
    });
};

osjs-client/src/adapters/vfs/system.js

    capabilities: () => request('capabilities', {}, 'json').then(({body}) => {
      return body;
    }),

But server-side needs path argument to find the mountpoint here. I 've tried to solve it, but did not come up with solution!

[mahsashadi]

@andersevenrud sorry for re-mentioning

[andersevenrud]

Closing because #804 superseeds this and there's already an ongoing discussion :)