fix: edit project metadata bug

[ciyer]

Fix bug that prevents editing of project metadata.

Fix #427.

[ciyer]

Can test on https://sekhar.dev.renku.ch. May need to reload the page, as the old logic may be cached.

[lorenzo-cavazzi]

It works for me.
There is a minor issue: project tags are not updated in the projects list -- this is true only for "starred" and "your projects", but it is related to #408 and the logic behind those 2 tabs need to be updated.

P.S. It may be a good idea to add a margin under the Update button. I added this in another commit, feel free to throw it away if you don't like it.

[ciyer]

Thanks for fixing the spacing. Looks better now.