Add-max-displayable-elements

[Th0masso]

Add the "maxElements" option to set a maximum number of displayable elements in a select to avoid performance issues. Also add the "maxElementsText" option to show a disabled option with this text as the last element of the select (if the limit is reached).

Please read my code and tell me if i have to change something, i really need that feature to be in the next version !

[Th0masso]

Hello @istvan-ujjmeszaros , can you check this pull request ?