Improved support for Contao 3.1

When using columnFields options_callback, it doesn´t pass an instance of MCW because new method getAttributesDca() is static and therefore expects DataContainer as additional parameter.
validate min and max count
fix js messing around with the event handler stack when destroying the
DOM-Element while the stack is called
Merge pull request #109 from backbone87/fix/min-max-count

fix js messing around with the event handler stack
Merge pull request #108 from backbone87/feature/validate-count

validate min and max count
fix mcw.js in FE again, unchecked "Backend" object access, manually
patched minified version, TODO repack
Merge pull request #110 from backbone87/dev

fix mcw.js in FE again
Minified js
Merge pull request #104 from w3scouts/dev

Improved support for Contao 3.1
Fixed method call
Merge pull request #112 from w3scouts/dev

Fixed method call
Add support for mcw in mcw.
Change tabs to spaces.
Merge pull request #114 from stefanheimes/dev

Add support for mcw in mcw.
Fixed exec error #115 & #105