Finish converting unit test suites to shared suite

This PR finishes the works started in #42 and moves all tests for the FSP events into a generic top-level unit test suite that can be imported by every provider.

Before this can be merged, some bugs need to be fixed. For example, as described in #8, the WebDAV client does not return the correct size of a file in the metadata call, so the shared test breaks for it.

Closes #18
No, range a generic HTTP for any data sent over HTTP. Sending these headers to the WebDAV server alters which bytes are sent back. This is actually better than the old solution, which fetched the whole file from the webdav server and then sliced the arraybuffer according to the range.