Add really experimental string support to WheelyWheel

[Bitl]

Attempt to resolve #5.

This adds an additional string value to GamepadUIOption, allowing one to use a string value alongside or to replace the nValue variable.

Alongside this, the usesstring value has been added to allow the WheelyWheel element to read the value as a string and not an int or float.

Why is there a seperate value? This was done to reduce the amount of conflicts. The nvalue statement also works as an index, so you can iliterate through values with usesstring.

this is extremely experimental, but works fine in testing.

[Bitl]

I have removed the string value from userdata and moved it to the main definition of GamepadUIOption for ease of use.

[DasMaddi]

Going to ask for @Joshua-Ashton to take a look when he has time, due to the number of changes involved in this one, I do not want to approve it by myself.