Proposition of extra functionnalities to existing files, new features and dedicated examples

add a remapSlider method used by some GraphicsItems in the functions file, add some extra functionalities to the InfiniteLine and LinearRegionItem items, add a InfiniteLineLabel item, a LinearRegionItemLable item, a CrosshairLabel, a new CounterSlider widget add four dedicated example (on per new item) and modify the __init__ file in the main directory to import the four new files
I know InfiniteLineLabel and LinearRegionItem menus are quite similar. However, the way we use them is somewhat different. For example, whatever the object clicked on (rectangle or the two InfiniteLines) for the LinearRegionLabel item, the menu is global. Of course, it is not sensibly different from the menu of a InfiniteLine (the main difference is that the bounds applied to the two InfiniteLineLabel), but I was not able to do other way. If you have any advise, I'm all yours. Similarly, I would like to add a global menu for the CrosshairLabel item and I was thinking of doing something similar to what I already did. Here again, advises are welcomed