Broken positioning of xtree finder suggestions

I noticed quite a few problems:

• the position of the dropdown used to show the tree finder suggestions; the default absolute positioning of the search suggest dropdown doesn't work well with the fixed position of the Bootstrap modal
• the suggestions were fetched using Solr without enabling prefix matching
• the finder suggestion dropdown remained visible after closing the modal (e.g. using the Cancel button)
• the keyboard event handling on the finder suggest input was broken (it was listening to keypress event which has become deprecated in the meantime and is not fired any more for non-characters keys); you couldn't close the dropdown using ESC and you couldn't select a suggestion using key down/up
• ESC key was closing the modal, which is not right when you have input fields on the modal

I fixed all of them.