Incorrect built-in scalars

[stuebingerb]

KGraphQL currently defines the following built-in scalars:

STRING
SHORT
INT
DOUBLE
FLOAT
BOOLEAN
LONG

However, the spec defines the following:

Int, Float, String, Boolean, and ID

According to the spec, those must be supported and also behave in a special way during introspection (which likely is not correctly implemented either).

So:

• ID has to be added (cf. Add ID scalar type to BUILT_IN_TYPE aPureBase/KGraphQL#173)
• Short and Long have to be removed
• Handling of built-in types in Introspection needs to be analyzed and fixed if needed

IMHO, Short and Long can still be included as built-in "extended" types to save users of the library from having to define them on their own but they must not behave like GraphQL built-in types. We can then also think about adding other common JVM types to those extended built-ins.