Search boxes for datasets & workflows on the project page

[jluethi]

Depending on how useful the search boxes are on the project list page (see #382), we could also add search boxes for datasets & workflows on the project page (after unifying the "create button" approach, see #383)

For this page (no mockup made so far)

[zonia3000]

New search boxes (f677e28):

[jluethi]

That's great!

Looking at it, we can probably drop the breadcrumbs on the project page, because the only thing one can do is go back to Projects, which has a top-level link anyway