Fix drag and drop in Compose

[wesleybl]

• Fix RuntimeError when dropping an image from a list tile to a banner tile.
• In PersistentCoverTileDataManager set, purge tile after put values into storage to prevent old values from being cache, since purge accesses tile.data. Also updated the attribute where data is saved for self.storage.
• Reorganizes the js events register in Compose when we drag content from one tile to another, in order to prevent the content from remaining on the source tile.

Fixes #914

[codecov-commenter]

Codecov Report

Merging #915 (a04ca0e) into master (900feae) will decrease coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #915      +/-   ##
==========================================
- Coverage   85.27%   85.25%   -0.02%     
==========================================
  Files          46       46              
  Lines        2825     2828       +3     
==========================================
+ Hits         2409     2411       +2     
- Misses        416      417       +1     

Impacted Files	Coverage Δ
src/collective/cover/tiles/base.py	87.71% <100.00%> (ø)
src/collective/cover/tiles/data.py	100.00% <100.00%> (ø)
src/collective/cover/browser/scaling.py	59.57% <0.00%> (-0.71%)	:arrow_down:

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