Improve FDT manipulation

[fho4abcd]

Functional improvements to fdt.php

• Drag&drop is enabled. Including moving multiple lines
• Minimal layout changes

Functional improvements to fdt_short_a.php

• New look applied, also for subwindow

• Remarks to indicate how subfields should be manipulated

  Coding improvements

• Removed unused code + equalize functional equal code
• Moved really equal code to included files.