reordering of labels in the label panel

[vanoudh]

copy of wekan#767

version : old wekan, wekan:0.11.0-rc2

on the label panel, the labels appear sorted by creation date
it would be very nice to be able to reorder them manually, like we can reorder cards in a column
or more simply, have them ordered by color then name
the same order should be applied in the "filter cards" menu

[xet7]

Moved to wekan#767