[3.4] File manager improvements

[lenvanessen]

Fixes:
#6758, #2263

Currently:

• Transforms body into dropzone for file uploads + adds dropzone hint on drop-event
• Moves event-handling handling outside of twig templates
• Improves the lay-out by moving the buttons to the right, instead of the bottom
• Lazy loads images, instead of pulls every thumbnail in when loading the page
• Adds search to the filemanager page

Test away!

[CarsonF]

The code looks good! Great job man 👍

[CarsonF]

I don't think any of these filters are needed.
Why limit the filename?
The |shy filter isn't needed as this is data not display text.
The |trim filter isn't needed as filenames cannot contain spaces.

[GwendolenLynch]

Why limit the filename?

I believe this came down to a the way BUIC handles things currently.

[lenvanessen]

Did not see this earlier, sorry about that.
Currently the filename itself is trimmed down in the display, for BUIC as wel as the filemanager.

It comes down to this, if the filename in the data-attribute would be the original (if longer than 80), than you'd get an inconsitancy in the display, the marking, and the search.

If you'd copy paste a filename in that is longer than 80 chars it would be found, but not marked.

If we'd remove the trim, we should also remove it for the display, so they are consistent. Simply left it there because I don't know why it was put in in the first place.