Permanently remove the systray

As it is not used anymore, remove the systray. This was cluttering
source code, was confusing people and this remove a dependency on
prototypejs.

This should help to load the page faster, which is an acceptance
criteria of story #7511: Drag'nDrop backlog items on Planning v2

Change-Id: Iee239d9a3ef2ba04e96fda00b820addbf8c3bd5b
Merge commit 'refs/changes/74/3274/2' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  Permanently remove the systray

Change-Id: I33a94a857aed7136b41d90a2179a86dc2954d7ce
This is Tuleap 7.7.99.24

Change-Id: I61912124b669e9465b45a74984bfcc4a91a64ca3